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I think the 1d8 extra necrotic damage could be pretty powerful against a tough opponent - good for a boss fight.  My bard's rapier would now do double damage.  And it uplevels the damage from spells like Thunderwave or Shatter against that target.   But my favorite would be that Dissonant Whispers gets a bigger boost: cast at 1st level and on a failed save it would do 3d6 + 1d8; that hits pretty hard for a 1st level spell.

anything that deprives you of your ability to take actions also prevents you from taking a bonus action.

Oh? Nice, I like that.

Let's have more discussion about this part:

At the DM's option, you may choose an alternative curse effect, but it should be no more powerful than those described above. The DM has final say on such a curse's effect.

Back in 2006, Dragon Magazine #348 offered a list of ideas for "alternative curse effects".  It's for an earlier edition of D&D, so many of the mechanics won't port over directly to 5e, but it's still good for generating ideas.

• I really like the idea of making it so the creature cannot tell a lie.  It's like zone of truth, but it follows them potentially for a very long time.  Probably less funny than the movie Liar Liar, but still a major social handicap once people figure out what's going on.
  
  
• For the right enemy, losing all armor and martial weapon proficiencies would be crippling.  Per the PHB p. 144, "If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells."  And subtracting the proficiency bonus from every attack they make with a martial weapon, if it's compounded with disadvantage on the attack roll, is a massive debuff.  You'd practically be one-shotting a death knight: no spellcasting, loses advantage on STR and DEX saving throws from Magic Resistance, its triple longsword attacks drop from a +11 to hit to a +5 to hit with disadvantage, and disadvantage on STR and DEX checks like to avoid a grapple or shove or break free of a web or telekinesis.
  Things aren't much better for a storm giant, an erinyes, or a skeleton lord.  Brilliantly, a drow inquisitor can't cast dispel magic on itself in this situation.  The trouble is getting them to fail that first Wisdom save.  Expect creatures with a legendary resistance to burn it on this.
  
  
• Increasing all damage from a specific source like an uncommon metal (silver, adamantine) or a specific element (fire, lightning, etc.) by 5 could be nice if your crew is all outfitted with silvered weapons and ammunition, or if a few of you have things that deal the same damage type (e.g. scorching ray and a flame tongue blade).
  
  
• Another socially devastating one, and potentially solid in combat against a "leader" character like a hobgoblin warlord or a drow house captain: "Everyone who knows the target no longer recognizes him, except for the caster.  Even the target's allies do not recognize him and those who come to know him again forget knowing him each morning."  That is brutal.  Sudden isolation.  For BBEGs relying on their allies, this is unacceptable.
  
  
• Forcing a target to carry a specific (not dangerous) object you hand to them or else suffer a -5 penalty to all saving throws is so flavorful, and for some creatures it forces painful choices: drop my weapon or shield, or take a lot of risk from whatever spells come next?

Another potential source of inspiration is the curses used by the Vistana in Curse of Strahd.  All of them deal psychic damage to the caster when the curse ends, depending on their power, but one of them does 3d6 damage even though it replicates the first curse in bestow curse (disadvantage on ability checks and saving throws for one ability score) so maybe tone down the damage.

• The target can't perform a specified act requiring fine motor control, like playing an instrument, writing, tying knots, or casting spells that have somatic components. (1d6 psychic damage)
• A nonmagical item in the target's possession (chosen by you) disappears and can't be found until the curse ends. The lost item can weigh no more than 1 pound. (1d6 psychic damage)
• The target is blinded, deafened, or both. (5d6 psychic damage)
• The target's attunement to one magic item (chosen by you, unless you want to leave it to the DM?) ends, and the target can't attune to the chosen item until the curse ends.  (Also 5d6)

Not being able to cast spells with somatic components cuts down the list by so much that it effectively shuts down most casters.  Not being able to play an instrument is the death of a bard.  Blinding and deafening a creature would be a nice upgrade from blindness/deafness.  Forcibly unattuning a magic item could be the turning point in some battles, and it doesn't have to be the Hand of Vecna.

Anyone know why bestow curse needs to be a 9th level spell to be permanent when the level 3 version was permanent in previous editions I feel like that is a bit much.

Dragon Magazine #348, page 34

Quote from Zarohk >>

The wording "choose the nature of the curse from the following options" sounds like it can inflict multiple of them, otherwise the wording would be "choose the nature of the curse from one of the following options", or otherwise indicate only one.

I might be mistaken for, but if there is no rule against how many curses a character can have, then you can stack this if you cast it at 5th level or above, since it doesn't have concentration tag. You have to spend multiple rounds to do a complex curse but you can just roleplay by chanting the curse and every verse applies that affect.

They can't give this to Sorcerer because Distant Spell and Quicken Spell, lol!

Wait! Does casting it at 5th level mean multiples curses on the same target stack?

RPGbot did the math on this: disadvantage is roughly equivalent to a -4 across all levels, with +/-1 at proficiency extremes.

Disadvantage without proficiency offsets anything more, closer to 5~6 point difference. 

As far as your last question, you choose 1, not all options, per the spell:

"When you cast this spell, choose the nature of the curse from the following options:"

So one of my party members asked me if he could have a curse that neutralizes healing. I was like "Sure". Not only that, but i made it so that if he gets hit, his wounds cant close and his blood wont stop. Essencially it means that If you get the tiniest cut when cursed by a level 5 spell slot, you can essencially slowly bleed out and there's nothing you can do about it. Sick. :D

but what if i want to curse someone with the curse of the etearnal stubbed toe

If remove curse can remove lycanthropy, can bestow curse bestow it?

What happens if in that short period the temporary lycanthrope infects someone?

• Does this spells effect proc once or 3 times on the base cast of Magic Missiles?
• If your summon attack the cursed enemy does the target suffer additional 1d8 necrotic damage? 
  • what if it was your hoard of undead skeletons that was the one who is doing the attacking? Do they still count as your spell?
• What of AOE spell that proc under specific conditions such as spiked growth?

Point 1 you make a separate roll for each dart so I'd rule 1d8 per dart. DM discretion though. Point 2 and 2.5, no, because it's not you attacking, it's a summon. Point 4, no as spike growth isn't an attack. 

THIS IS GOING TO BE FUN TO USE!!!

No

thats the point of save or suck spells, same for hypnotic pattern, banishment, dominate human, and dominate monster. throw monsters with better saves, or good bonus actions and reactions they can use.

Quote from HumanHornet8 >>

If a single person is casting multiple of the spell at low levels, no. Concentration spell. If multiple people cast it at low level, yes. If cast at high level, without the concentration requirement, yes, even by the same person.

I think. That's just my understanding of how it fits into the rules.

 Effects with the same name don't stack. Multiple castings of the same spell, etc. have no additional effect. 

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don’t combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

For example, if two clerics cast bless on the same target, that character gains the spell’s benefit only once; he or she doesn’t get to roll two bonus dice.

As always, your DM is free to rule as they wish, even against stated rules.