I heave read that Lima's prefer to be kept in groups
***Me too. Beware, 99%+ your LSN will turn out a Sorubim elongatus with a 1' max size.
, however my LFS got only one in so that is all I currently have.
***Perhaps a start. There will be more. The season is approaching and they are usually widely available.
I am going to put him in a 160g tank with some large, peaceful SA cichlids
***Which peaceful SA cichlids?
, and was planning to put a small group of Pictus catfish in as well. Would the Lima school with the pictus?
***Not in any schooling sense. May huddle up on the bottom once in a while but even similar-looking fish rarely school with a different species. Pictus do best in large groups of a dozen, BTW.
How big will he realistically grow?
***1'. Per above.
Should I try to get more Lima's
***Yes. Up to 4-6 at least.
or just keep him with the Pictus?
***If size disparity is great, I'd not. If a pictus is say 3"-4" and LSN is 5"-6", that's doable. A 2" pictus may get eaten.
Should I plan to move him to my 700g tank with big cichlids, Achara and Giraffe catfish when he gets big, or would that be a bad idea?
***If the cichlids won't prey on it, yes. Achara and giraffe catfish will not, in all likelihood, bother LSN. I've kept about a good dozen or more 1'-2.5' acharas. IME, they wouldn't touch 3" koi tank mates. Profound scavengers.