So it sounds like you really just need one crafting class leveled then? Which would would work best for all the things that Pyros mentioned? Armorer?
Overmelding gear is something that doesn't concern most people. Basically it's only useful when a new raid tier is released and only if you're pushing for full clear early. It lets you use the new crafted gear tier and overmeld it with materias to get an advantage on gearing up before you get enough drops from the raid. But for most people, they progress so slow it kinda doesn't really matter, and if you don't plan on raiding it literally does nothing. Also technically while it's better to overmeld yourself since it can take a while, you could just ask anyone else to meld for you. Note that most people will pretend they're afk since this shit is boring as fuck to do and takes a long time, but even for that you don't actually need crafting. Also you'd need several millions to overmeld all your gear properly for every tier, so even if you were to lvl a crafter it wouldn't do that much until you have enough ressources to afford the shit you want to craft and overmeld.
Also leveling just one craft can be very rough. Most crafts require materials crafted by other crafts. If you want to make a plate armor, you'll often need leather, cloth or jewels from LTW/WVR/GSM on top of your own metal stuff(also wood sometimes, and quite often in heavenswards and later Alchemy stuff). The only crafts that kinda stand on their own are Alchemy and Culinarian, Alchemy still requires various materials when making books but for the potions and stuff it's just raw materials, while CUL sometimes require alchemy stuff(salt and what not) but that's not that common either. On top of that you can't get good crafting gear without making it yourself, can use scrip gear but it's really not optimal(although it's "enough" for casual stuff).
As for repairing, you need the craft that makes the item you're trying to repair(unless they changed that too not sure). So for heavy armor you'd need an armorer, but often your legs are going to be made of leather or cloth so you'd need these, jewelry is often GSM or CRP but also sometimes LTW and weapons vary greatly. The only craft that doesn't repair anything is CUL.
Overall my recommendation would be to give crafting a try in the early levels, see if you like how it plays out, and then start leveling it casually using daily and weekly turn ins(daily GC turn ins, weekly custom deliveries once 51+, daily beast tribes once you get to Moogle ones since Ixal is kinda shit for lvling). Or you can just ignore it entirely until you have enough money to just skip most of the annoying shit. Crafting can be powerleveled in a few hours if you have enough money. Or just not do it at all, as I said it's optional and many raiders don't actually have crafting leveled at all, just don't forget to repair your gear before doing content(there's a warning when your gear is under 40% durability when you queue).
Kirun
I get it man, no worries. I just figured this Corona shit would have you at the house more than anything else, and it would be a good time to dive into FFXIV. $20 instead of $40 sounds a lot more attractive. MMO's have saved me a lot more than what I could have spent, however.
