Hey,
I don't find them too hard to get eating, although they aren't like motoros that just jump on food right away. I started with live worms for my tiger and flowers then moved on from there. The only problem with rays like these is that they are fairly unforgiving. They need very large tanks, very laid back (if any) tank mates, lots of water flow/oxygenation and extremely clean tanks.
I would start a twelve incher off in a 120 tank, or 4' x 2' bin as a quarantine tank, then move them into something minimum 6' x 3'. Then expect something wayyy wayyy larger. Once in the qt, you should treat for internal parasites, that is the first thing that would do them in.
I wouldn't mix with more aggressive rays (like black rays, motoros or pearls), or plecos, semaprochilodus, or really a lot of things.
Personally I would suggest Schroederi, very similar species and IMO much prettier as adults. They are usually available for much better prices, a little bit more forgiving and don't get quite as large either.
Good Luck,
Justin Morash