I used a Mega with it, but I had to shuffle some pins around (SPI interface pins are different) and that meant I needed another board between the two.. Sparkfun has some little Arduino proto boards that did the job nicely.
for screens, if you're looking at like the 3" color TFT touchscreens, I don't know how well they'd work, they take a whole lot of pins on the Mega, and it would also be a lot of processing power needed..
If you're well versed, or have the ambition to really learn the software/coding side of things there are all sorts of ways to work around it.. you already have CAN bus, so you could have a completely separate unit that does the display and transfers commands to, and receives data from the Lil'bb. That way a slowdown because of high display workload doesn't affect operation.
I just have a switch that changes modes.. If you had a dedicated display controller you could use a rotary encoder with a pushbutton to do all sorts of things.
'94 dodge, Colt Cam, head worked, NV5600, 3.55's, SB clutch, Ford manual hubs w. hawk brakes, custom flatdeck, custom aluminum bumper, cab off restoration, totally new engine, Mahle pistons @19:1..HE351VE with 67mm turbine and 67x95mm compressor
440hp/1000 ft lb @ 2400 RPM