They are definitely evil, but I like them. :twisted: They are cute! They have those bony fins and sparkly pink scales. They aren't quite pretty but you can't say they're ugly.
I've had two for about 4 years. But I can't really answer your questions definitely.
Do they eat plants? Mine seem to be particular. They do like the very small floating stuff whose name I don't really know. They don't eat fresh (terrestrial) veggies or fruit, though. I haven't had a large variety of plants in their tank to really be able to conclude one way or another if they'd be bad overall for plants. They are definitely not as plant-eating as large common plecos and they are gentle (non-spastic) and coordinated and not inclined to uproot things.
Do they pester other fish? Mine have at various times lived peacefully with angelfish, bettas, plecos, chinese algae eaters, and some goldfish. The only badness towards other fish is a periodic chasing of a very large goldfish. They don't seem to hurt their victim, but they harass her cruelly. They never pick on small goldfish. They don't really belong with goldfish, of course. I also suspect they might have snipped an antenna off an apple snail, but I can't prove it.
I got mine at the same size and the same time and I do not know their genders. They do kiss, but they also act sort of romantic at times (times that suspiciously coincide with goldfish-chasing behavior) so I suspect they're a pair. They also do not maintain distinct territories, but instead stay close to each other at all times. Sometimes they chase each other, but it's not aggressive. Rumor has it that the kissing is a territorial display between two males, but I'm not convinced. It's supposed to be as close as they get to fighting though, so it's possible that 2 males could coexist--some think it's desirable so you can get the kisses. I'd try to get similarly-sized babies.
In general, I think they'd be fine in LARGE community aquariums if they have a place to hang out. They like to keep to themselves. I believe mine get aggressive periodically because they want to nest and they don't have enough room because I haven't gotten them a new tank yet.
Mine haven't been in with bite sized fish since they were themselves bite size, though, so I don't know if they eat other fish. I would love to know if anyone has had their pinkies eat small fish! I want to use a pinkie to clean up and desnail a tank with danios, but the danios look so yummy, I'm afraid to try it.
The only problem I have with them is that they're so darned BIG. You can see all their teeth without looking very hard. Just big pink flat fish. (That eat hydra.)
My big pink fish are available for a free trial if you live near SE Michigan. That's what you need--a trial to see if they'd work for you!