I had 4 silver dollars in my juwel vision 260, I rehomed them as I felt there wasn't enough room for them. They often went smashing into the sides if I was doing a water change, or walked in the room. They do get to the size of a side plate and need room to swim as they are active fish.
I would instead try and search out spotted silver dollars - they stay smaller (can have a larger school) and are more attractively marked in my opinion, males especially. They are relatively cheap as well, I think my LFS has them in at £3.95 or something similar.
Stocking can be pretty open with silver dollars, they could be the main attraction with a school of smaller tetra such as neons/cardinals, or they can be 'dither fish' for cichlids. I'd go for a South american theme personally. Sandy substrate, winding pieces of bogwood and a few hardy plants/mosses (as you've heard silver dollars are renowned for eating plants, mine didn't touch onion plants or java fern/moss though so they might be an option - I wouldn't do a rocky theme though as I think it would look unnatural personally, they might also scrape themselves on the rocks as they are skittish). For fish I would have 6 spotted silver dollars, a shoal of 12-15tetra's (rummy nose/neons/cardinals/blackwidow tetra) only 1 shoal though as I think a large school looks more impressive than lots of little shoal. For the bottom I would do 8 corys and a pair of dwarf cichlids (apisto's or rams).