thepitclub,
Are you more interested in wintering fish or water lilies? I've done both using the 100 gallon stock tanks. When doing fish, I only had babies (less than 8" long) and used "in tank" type filtration. I used a small pump at the bottom of the 100 gal tanks, and pumped them into a DIY mechanical filter/ Trickle tower filters, suspended over the tanks. Worked like a charm. By the time the water passes through a filter mat and the Bio Balls, it is perfectly clean. Never had a bad reading. When doing lilies, all I have are strong lights suspended over the water, and bubble stones. Maybe a couple tiny fry from the season. Lilies (tropical) need more light that that in my hated zone, so my next expenditure will be the metal halide lights.
It's not too big a deal to rig up anything you need. If the holes are 2", even easier. 2" plumbing/bulkheads/fittings are much easier to obtain than 4".
Sounds like a pretty good good deal. I pay 65.00 for one 100 gallon stock tank around here, on sale.