In your position, here is what I would do: buy a 2- rail Williams 0-6-0 off of eBay for around $300, some cars from the used market or Atlas industrial, and some snap track. Put a Radio Shack bridge rectifier on the output of your simplest transformer, and a DPDT switch for reversing. Set it up on the rug, run it, and see if you like 2-rail. If you don't, then sell it and press on. Shouldn't cost that much in the end.
I have three of those B6sb Williams switchers, and think they are great. One had tinplate flanges, but all are now 2-rail. Cheapest was 175, most expensive was 300.
I have a few plastic freight cars, used mostly for engine break-in when I want to run light, but still watch a train. Back in the olden days they were a buck each, but you had to trim the flanges and add scale couplers.
