silver sharks will eventually get 2 big as well bristlenose plecos are a good choice for a sucker fish look almost like a big pleco that will get to 40cm but they only gt around 12 or 13 cm . take into account stocking levels and plan for the future . 1 cm of fish per a litre is the ratio i think(some1 correct me if im wrong) and i think a ar620 is 160 l (again correct me if im wrong) so that mean 160 cm of fish but does not mean 4 x 40cm plecos either! big fish need big tanks and some small fish will get big fast Take silver dollars for example so weork this out on the maximum size the fish will get ,not at what it is when u buy it.
the other thing is to avoid aggressive species of fish unless the tank mates are able to handle them. so pays to do ur research . having guppies and neons and other small fish (or having angels bigger gouramis etc) can limit the variety of tank mates somewhat as the small fish arent going to last . find some fish u like the look of on the net or in an lfs and find out if they are compatible in terms of water chemistry(no use putting a discus with africans etc) , behaviuor and size of the tank if u get stuck on certain type ask on the forum by the way great to see ur native tank doin well and that u have contracted MTS