I'm not very good at soldering so for me it's very hard trying to solder my wires to the tiny pads on my FC... So here's what I got so far - the square pad above the 5v wire right in the middle has a tiny bit of solder on it that I don't know how to get that off... is that bad? I don't plan to use that pad for anything. Will that cause a short or anything? Anything specific I should be checking for on my multimeter to make sure my solder job isn't causing any shorts?

You can use the DMM to check continuity to avoid short.

You have too much wire stick out. Cut away less silicone. Your solder looks dry.

Solder on an unused pad is no problem as long as it's not a huge blob that's in danger of deforming and causing a short. You can either clean off any excess with solder wick (put some flux on the wick first) then press it onto the pad and it will suck up the solder which will get transferred to the wick. Alternatively just put a dome of solder on the pad to leave it looking neat.

To echo what Voodoo said, your joint's don't look particularly good so I those are something you definitely need to try and improve if you want headache-free electrical issues. If you're you're using lead-free solder then get rid of it and buy yourself some decent quality 60/40 or 63/37 proper leaded solder with a flux core. You need one which has a 0.4mm - 0.6mm diameter for the kind of electronics we work with in this hobby. The brands you want to be looking at are Kester, MG Chemicals or Multicore (Loctite). Try to avoid any if the unknown quality Chinese or no-name stuff. You will pay good money for the decent branded solder but it will improve your soldering ten fold and it generally lasts a long time, so it is money well invested. Also, make sure you use plenty of flux while soldering. You can never have too much. Just clean off any excess afterwards with a Q-Tip and some Isopropyl alcohol.

+1 better solder
i would say good solder do 90% of the solderwork for you, while bad solder can make it impossible. i will never try to save money on solder. get good solder and join the solderpleasure ;-)

oscars solder instructions; https://oscarliang.com/soldering-guide/