your 2014 mbp (11,1?) either came with 8gb or 16gb of ram from the factory. there's no way to the user to add more after the fact. you could pay a microsoldering shop to add more, but that's not usually worth the cost. you could have someone drop in a replacement logic board with 16gb already on there but that's like $150.

it's a decent job, but here's the replacement keyboard. That same site has the battery and it makes sense to do them at once since you gotta pull the battery anyway.

the battery is glued in, so if you're not comfortable dealing with that then a repair shop is your best bet to install a replacement keyboard and battery.

you have a mac, so maybe a good place to ask for help with opencore is the lemmy.ml apple community.

e: i think i understand what youre asking about the opencore legacy patcher... you want to make a bootable patched install media but you can't because you can't boot into macos to make it, right? you'll either need to start back from recovery boot from square one and lose your linux install or have someone with a mac either make you an opencore patched install media for your model or supported vanilla install media (in your case i think that's macos 11 big sur) that you can install and make an opencore patcher to upgrade from.