As for the expression pedal, I have such thing from M-Audio and it works well. I tried FC-7 and it didn’t seem to me to be much better. Actually, the one from M-Audio let’s you to change its straight by turning a small wheel on it. You can make it to change the volume only slightly, not the whole way.
Hey, whatever works for you is best...I just happen to like the FC-7 and I'm used to it's response....M-Audio make some great stuff.
I find the volume pedal essential for my playing style, which is primarily instrumental music...perfect for swells on strings and organ, and also a nice way to add extra expressiveness to reed and brass instruments...nice on Distortion type guitars as well as Pedal Steel.
Getting the proper RH/Accompaniment balance comes with a lot of practice and getting used to the lead sound buried further in the mix when playing "live'. It took me awhile to get used to it, but my one take recordings were much the better for it, as well as the "live" results to the audience.
For recording, the fix is much easier, for, as you say, it can be fixed in the mix-down process. Of course, then you don't have as much control, unless the lead tracks were recorded separately.
Still, I must say your playing is very good, with lots of expression...I worked as a Yamaha demonstrator/clinician for well over 20 years, and it was a very rewarding and interesting job. I just retired a few months ago.
Good luck with your endeavors.
Ian