Harder to find small ones (4" ) when they really look stunning. Also find that marble achara are slightly more common small than sailfin achara. Have been a few larger ones (14" ) for sale on Aquaristclassified recently but thats because they stop looking quite so cute and folks start realizing that with them whiskers and growing to 30" you will need an 8 * 3 tank ideally or a pond so his whiskers are not always touching the sides. (Never seen it done but that 4ft cube could house him alone until over 2ft mark).
I have a marble and would get a sailfin if I saw small ones available. Pier aquatic s tend to get them in a couple of times a year, but only in small qtys. Probably see less of these now here in the uk than piraiba which is wierd, considering the final size of piraiba.
Have seen sailfins kept with neons and community fish, although I would not try it, they are said to be much less predatory than marbled.
PH of 7.5 and under, temp late 70's should be fine.
Unfortunately you may see his marbled and lightening pattern fade somewhat with size and age.
Great personality fish which you will be able to train to hand feed as a pet.