1. The standard 40x60 is made up of eight pieces of O36 curves and four 10" straight tracks. One of the straights is a terminal/power connector track where you connect your transformer. You can find this oval of track on the big auction site all day for about $60.00 shipped to your door. It will cost about the same buying from local hobby shops or other vendors. - - If cost is a major concern for you, you can save a couple bucks by purchasing brand new, tubular style, track from Menards, which will cost you about $32.00 if you have it shipped to a local store for pickup. (As a side, at the moment, Menards is stocking a 4 pack of O36 Fastrack curves for $13.99, but I did not see and straight track available. ) You can also buy boxes of dirty, but not rusty, used tubular track very cheaply on the auction site.
2. Almost any lionel transform made after WWII will do the job with the addition of a modern, fast acting, circuit breaker. The DC wall pack that comes with starter sets, however may not be the best choice for a LC+ engine. Some of them do not have quite enough power to fire the electro-coupler on the engine. My top choices for running just one LC+ engine on a small oval of track would be a Lionel CW-80, An MTH Z-Controller with any of the various power bricks made for them, or a post war 1033 with a modern circuit breaker installed. You may find a postwar ZW or KW really the most cost effective solution, however. Asking what transformer to use is a fairly loaded question as there are many things to consider including if you plan to expand the size of your layout, have parallel tracks, powered accessories or other thing that may demand a bigger transformer. You also have to consider how handy you are with wiring and basic electronics: if you are a little handy, adding circuit breakers to postwar transformers is simple, but this is a nonstarter for some folks. Last, there is brand preference/bias, and tall tales of particular models being unsafe that are practically identical as far as safety design with other models touted as being the best choices.
3. Postwar cars will work just fine on fastrack, and with the LC+ engine and its coupler. The problem you may have is with the lights, for two reasons. First, if you use a small transformer, or one of the LionChief wall packs, it may not have enough power for the high demands of the light bulbs. Second, if you have the track set to a recommended 18VAC constantly on, on the track, you'll burn out the postwar bulbs. There are several good options to fix this, including installing higher voltage bulbs, but the preferred method is probably to install LED lighting in the cars. LED lighting will also eliminate the 'not enough power' problem as well.
So what to do? If you are on a serious budget, I would do one of two things. First would be to buy a good, used, postwar transformer and brand new tubular track from Menards. The second option that makes some sense, is to buy a starter set that has some cars or something you like in it, keep the track and transformer, and resale the engine and anything else you don't want on the auction site. You can pick up good LC starter sets for as little as $200, and likely sell the locomotive alone for about $100.
JGL