That's exactly what it should be, all planted, or dare I say thoroughly planted (the more the better!), drift wood and rocks are not very relevant, but if you like the loot better that way, it won't bother them one bit
Don't hesitate to "overplant", even if it seems very dense, it'll be fine, they can squeeze themselves through anything 
As for bottom feeders, the rule is the same, especially pictus, because if they try to eat them, they'll choke and won't be able to spit them out because of the barbels.
290 litres is a nice volume for bleheris, I had 6 in 100 liters, until a pair formed up and I had to move them. I assume 6 can live in a 290, and even if a couple forms, there is a chance they can cohabit in that much space.
As for bottom, sand or gravel doesn't matter much. I had a sand bottom covered with rocks and they were fine with it.
As for bottom feeders, the rule is the same, especially pictus, because if they try to eat them, they'll choke and won't be able to spit them out because of the barbels.
290 litres is a nice volume for bleheris, I had 6 in 100 liters, until a pair formed up and I had to move them. I assume 6 can live in a 290, and even if a couple forms, there is a chance they can cohabit in that much space.
As for bottom, sand or gravel doesn't matter much. I had a sand bottom covered with rocks and they were fine with it.
