The nice thing about starting with powered track is you can always switch to on-board battery power later if you want.
I highly recommend putting your track on some sort of subroadbed support --the ground can and will move around a surprising amount. It's nice to be able to go out and run trains without having to deal with track that has shifted on you during the winter. Or heavy rain. Or hyperactive squirrels.
Laying a proper foundation is a lot more work up front, but it makes for much easier running in the long run.