SOOO much to DO even on a 4x8 it can be absolutely overwhelming! IF you let it! Track, scenery, electronics, rolling stock maintenance, loco "hiccups" MISCELLANIOUS!
WHERE to START? "strokes for folks" as usual, it DEPENDS on "what you want to see" first, trains, or scenery.
I'm sure I'm not alone in wanting to see trains running through scenery, but as anyone who has done this for any length of time will tell you, "ya can't have it ALL, all at once!" Choices and priorities are as different as the layouts that require them. Whatever it is, I say GO for it!