How much power do I need?

How do I know how much power I will need for my layout? 

It all depends upon the sum of the individual power requirements of the engines, lighted cars cars, switch tracks and accessories you plan to operate simultaneously. You should plan to power switch tracks and accessories separately from track power.

Do I need to use more than 1 TIU to operate the trains, switches and accessories?

You'll need one AIU for the first 10 switch tracks and accessories that you have, and another AIU for the next ten, and so forth.

You'll need more than one TIU only if you have more than 1,200-1,300 feet of track (approx.), or more than 50 switch tracks or more than 50 accessories.

Thanks for all the info Barry!