Need Guidance

I am just getting into trains more or less. I've got my old Marx NYC 4000 from when I was a kid but I am wanting to build a larger layout. I am interested in what kind of track has the best results. I have looked at some of the Lionel stater sets with fast track and a train in the $250 - $300 range. Is this a good place to start or should I just buy it piece by piece to begin with? Will Marx trains work OK with Lionel track or are there problems doing this? Are train shows a good place to buy or can I do as well on the net?

Thanks!