Thank you to all who replied. I will consider all of this in my future purchases.

I am interested in getting into model trains. I have liked them since I was a youngster, and now I feel comfortable spending time and money on it. I bought a small starter set: Lionel Pennsylvania Flyer Freight Train Set, and I have realized since my purchase, that the HO is a more popular scale. My question is; Will HO and O work on the same track, and will Fast Track work with EZ Track, and what tracks are compatible. I would like to fill a 12x12 room eventually.
I would also like to  know a good resource for trains, tracks, accessories, etc...
What kind of trains should I be looking for? Is it a mortal sin to mix and match?
Any help will be greatly appreciated.

Thanks
Greg G
Germany