Final Cut Pro is a known VERY good app, tons of features and stable. I just looked at your When the Saints... video... IMHO background too busy, and your head and accordion are cut, but even at that, technically, your best video to date because we can see you and the accordion perfectly clearly. It makes it much more personal for the audience that way, and they see your accordion up closer than before too!
Does your accordion have internal mics (I am quite sure it does, but want to ask anyway)? Do you not connect those to your input device? If you order a 4 input channel, that means you can do a L/R digital side and L/R acoustic side and manually balance everything off in an external audio software then paste that in to your video editing software (I use Reaper). However, there are very few internal mics that can compare to quality external mics, which is why I invested in external mics, but those can get expensive easily too, though anything above the $200 each starts to sound quite decent. That said, I have an ongoing project to make my own custom internal accordion setup one day, just to play with, and again, learn.
For acoustic recordings, I played with ElCheapo ($20 each) mics and had pretty good results, but then I went way overboard
, and chose 1 condenser mics that were $1,000US for a matched pair of seElectronics SE4400a condenser microphones.
Expensive, yes, but the sound is definitely high end studio quality and they sound better than mics twice their price. Once I get my Hohner Morino tuned (in a couple of months), I will start making some acoustic recordings using this setup. In the meantime, I am learning about mic placement and styles. If that interests you, I have
a blog post about a couple of excellent setups for the acoustic accordion using external mics.