Well, of course soundfonts will make a big difference in sound quality. They're much better than basic general midi since they have higher quality samples (for the most part) and will usually make midi more tolerable just messing around with the base midis and replacing the instruments with soundfont instruments makes a huge difference and it goes from being okay and tolerable, to great and epic in a few seconds. And it makes your own pieces that much better when you use a soundfont especially if you're going after a specific era.

I believe the piano glitch was there in the unofficial RM2k3 and from I was reading you need to do some stuff to the MIDI track in Audacity to fix this. I'm not 100% sure how to fix it, but I'm sure there should be a solution on the internet somewhere.