Hi Jason,
Welcome to the hobby, couple recommendations for you when you move to the big tank. Unless you are going for the length go for either a 120g or 4' 150g, if you are going for a reef tank, you will find the 24" deep tank much more desireable. If you are going for the 6' length, go for the 180g, same length as 125, but 24" deep.
Also, if you haven't already, I would go ahead and join WAMAS and check out the for sale items, you'll find you can find just about anything you need there and if not, you can post that you are looking to buy something specific.
Kevin