Trying to create a kit that has bass, horns, strings and keys - I’m finding it impossible!!! Any ideas 
It’s technically possible, but you will be severely limited by the number of available notes (128) that you’ll have to share across all instruments, and file size limitations for the drum kit, which has to include all the wave files.
So, I’m going to go with no, it’s not practically possible within those limits.
It’s possible. Make the bass only 1 octave. Use the lower end of the midi range for the keys, 0-33, that gives you almost 3 octave. Drums are still at 35 to 59. Put your bass at 60 to 71. You then 56 slots open for strings and horns. Run your horns at 72 to 100, and your strings at 101 to 127. Shift octaves as needed with your parts. Done.
Like I said, technically possible, but when you start adding the wav files, I think you’ll run out of room in the file.
That said, if @Phil_Flood says you can do it, I’d say that’s cause for hope.
I’ll give it another go - only a few more strands of hair to pull out anyway - it was neck length before I started
Thanks for the input guys