Can I use this on myself?

A creature you touch becomes invisible 

Are you a creature? Can you touch yourself? If Yes on both, then you can.

I really thought these were like private comments that we could use for our games. Le sigh. 🙄

What if that person is a ghost? Would the ghost just phase through themselves!?!? Is that considered touching yourself!

Yes. No. Yes, if you are said Ghost. 

Does it actually say that ghosts can touch themselves anywhere in the books?

"The spell ends for a target that attacks or casts a spell."

How about a Cantrip, which is technically not a Spell? 

Cantrips are spells, they just don't require a spell slot to be used to cast.

can this be a ritual spell

Nope. Your DM might create a ritual version as a homebrew option though.

So quick question about this spell. This spell states that anything that the target is carrying is also invisible and that if the TARGET attacks or casts a spell the effects end. So here is the question: If one was to cast invisibility on a horse wouldn't the people riding it also be invisible as they are being carried by the horse? Furthermore, because they aren't the target can't the riders of the horse be able to attack without the spell ending?

No, they would not.  This affects one creature and anything they are carrying or wearing. 

Quote from Danzilla >>

Does it actually say that ghosts can touch themselves anywhere in the books?

As a ghost, I can confirm this is possible

( ͡° ͜ʖ ͡°)

Can you turn invisible unwilling or hostile creature? The spell does not specify this.

I’ve always wondered if the person the spell is cast upon, if he or she can see itself? I’m thinking no, but that they’d have some sort of idea where their hands, feet and other limbs would be? It’s not described. So I’m curious of how others do it? :) 

Could Detect magic see an invisible creature?

invisibility is an illusion created by magic, therefore an individual using detect magic would sense the presence of the magic if it’s within range, but no you can’t see the aura because the person is not visible.

Detect Magic: “you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic”

How do we feel about using a magical item that produces a spell effect? Would this count as "casting a spell", or not?

 What is the difference between greater invisibility and invisibility?

And why does the 2nd level invisibility spell look more powerful than Greater Invisibility spell.

Greater Invisibility allows you to attack or be damaged while staying invisible (provided you succeed on your concentration saving throw).