MTGroove.
much as i love realband, i feel , from what youve described, and obviously i dont know all you want to do;
and given the midi file volume you have;
i would suggest you look at reaper that i also use.
(www.reaper.fm) because i find i can work very rapidly that way with reaps.
ie lots of midi clips/files...i feel you could save time.
just download the reaps demo. and run tests importing midi along timeline and lots of different traks etc.
its very easy to grab midi clips with the mouse n rapidly move around etc. i also feel reaps would handle such a big volume...run tests n see if it meets your needs.

best
om

my songs....mixed for good earbuds...(fyi..my vocs on all songs..)
https://soundcloud.com/alfsongs
(90 songs created useing bb/rb)
(lots of tips of mine in pg tips forum.)