So, l want to be prepared for any possibility l can think of (and ideally any l can't) so l decided to post this to ask a Hypothetical question: Should l allow Feats or Magic items at level one/start of campaign if the players backstory makes sense for them to have said feat or magic item, and they're not a race/class that would get them. (Ie, they aren't a Vuman 2nd level Artificer) (Yes, I'm using one of my characters for example. Though I'm adding some details for this hypothetical.)

For Example, l have a Human Necromancy Wizard with a 4 Str, (Rolling can give some wild results) despite their backstory having them be a Farmer, and the I want them to have a Homebrewed magic item that gives them a 10 Str, with the intention of it becoming worse over time, for story reasons. (To the point it becomes non magical/only gives a 4 Str, which is their base)

They also went to medical School (Necromancy wizard) and want the Healer Feat, despite not being a race that gives a level 1 feat. (This was true at one point, but they actually are a Vuman, so they already have this feat, and l won't bother asking if they should be allowed another feat, one for backstory and one for race, cause that's silly.)

So, as l asked before, Should l allow Feats or Magic items at level one/start of campaign if the players backstory makes sense for them to have said feat or magic item?

To be clear, know l should draw limits. I won't let them start with magic items higher than common/Uncommon, Rare at the highest if it makes sense, and no "powerful" feats like lucky or warcaster, but would it be reasonable for a dm to allow the "Farmers work gloves" or a more Roleplay feat like Healer?

Edit: I just remembered that the D&Done UA mentioned having feats granted by your background, so there is some precedent, assuming it survives the UA process. I Won't be surprised if there will be a official "Medic" Background that grants the Healer feat. Hell, the current version of the FARMER background grants the Tough feat, and Urchin gives Lucky, so the Healer feat shouldn't be any issue! Infact, Pilgrim gets the Healer Feat! Healer feat from backstory/background is almost official!!)

Well. if it was me, I wouldn't allow them to start with any magic items for any reasons.

Regarding feats, also I wouldn't allow feats because of backgrounds, I would either allow ALL players to begin with 1 feat at level 1, or deny all players that feat, except if they choose a race that starts with the feat.

Simply because I don't like the idea of rewarding creative players, that write massive backgrounds to get something not all would get.

Fair point. I would ask if it's ok with the other players first before allowing it.

Magic item is right out. Start down that road and everyone will write into their background why they have the family’s old vorpal sword. 
Feats, if you let one person, you should let everyone. Personally I’m not a fan, but there are lots of people that allow feats at level 1, and it doesn’t seem to break anything. 

I usually allow my players one free feat at character creation because I love feats. I've also gifted my players with free feats as a plot point. But what I do for one, I do for all. 

Magic items are a different beast. 5e is not at all balanced around them, and especially not at low levels of play. I tend to be pretty stingy with them, myself. If I were you and really set on running a high magic campaign, I'd either allow my level 1 players to choose from a curated list of magic items, or I'd dictate that the items had to be non-combat related or consumables. Even then, you need to be careful. I mean, an Elemental Gem is a consumable, uncommon item that would give level 1 babies control of a CR 5 creature. Talk about busted.

People should be building their background around the abilities that the game rules provide for them, including what is provided by their chosen Background.

There's no need to provide anything additional, and players shouldn't be writing stuff into their history which is item/feat fishing.

I've heard that the UA level 1 feats are weaker than the currently published Feats.

Quote from DnDNewper >>

Fair point. I would ask if it's ok with the other players first before allowing it.

No, don't ask the other players. If you're the DM, just make a ruling

There's no reason for one player to get a level 1 bonus other players aren't getting. For that matter, giving out a magic item at level 1 that removes the penalty from their dump stat is a bad idea, even if you are giving all the characters magic items. If you let the players roll for stats, and one got a set of stats you deemed unacceptable, either let them re-roll or come up with a different method of stat generation for everyone (there are options out there that keep the fun of dice rolling while still balancing things out to a degree)

Give everyone the same stuff when they start out. Otherwise, all you're doing is fueling Main Character Syndrome