I would recommend 6x2x2 for lima (get 2) or larger, forget the tsn till you set up a massive system (i know) you will always be able to pick one up when you want and probably for free if you adopt a big one.
My TSN went from 2" just before thanksgiving when i bought him to 10 maybe even 11" today. During this process he ate several tank mates who were bigger then him when i purchased him. I was under the impression that a 180 would work for life but im quickly realizing that wont work. Now im trying to convince the wife to let me use the tub in the master bathroom. Its a 5' circle that i would fill up roughly 2 ft high. Most likely will need to rehome him =/
Hi , Please dont get a tsn unless you can provide for it! as you have already been informed it will need a big tank.. but what really will need is thousands spent on building a suitable home and feeding it.
This thread shows you how its done IMO : http://www.monsterfishkeepers.com/forums/showthread.php?t=378921&page=7
By all means go for the lima it will be far more managable in the long run.!