your tank sounds about 125 gals (6x1.5x2) so you could keep up to 5 p's in there for life
i would tank the p's but add acouple more
alos to onion there isnt really anything you need to know (other then feeding and temp) when keeping p's other them general FW info like cycling , testing...
i dont beleive in the 2 # but if you want more i would get them at the same time as the others
dont buy them on their reputation or you will be extreamly dissapointed
if you take the P's all you will need to do is up the filtration (depending on your current setup)