If you decide to go with IM think long and hard about your overflow options. Most people go with external because it doesn't take away real estate in the tank. You must have your tank about 6" off of the wall. I'd go EXT if I was to get less than the 200g. I think the 200 internal is the way to go. I have an internal on my 130 and it chews up a ton of real estate. I love the durso stand pipe. It's super quiet. Also consider what they have in stock as well. Last week they had white 170g EXT in stock. They could take as long as 6 months to arrive. You could build an awesome aquascape with dry Marco rock and then dark cure it with 5% LFS rock and it would be perfect by then. All of the pests would be dead and you could drop coral in on day one. This is the best way to achieve biodiversity IMO. I'd assume that it would only take a few months. I'd call...
BRS has some excellent videos on building aquascapes. I highly recommend their extra thick super glue, the activator and then Marco mortar. You can go over the mortar with thin super glue and Marco powder. Check my build thread...
If you want to save money, there is no better bang for the buck than some used Hydra 52s on here for about $200. In fact, I recommend you buy everything but the tank from the classifieds here. You will save 75%! With a few months leadtime on the tank, you can aquire what you want... not whats available. I use the WTB and usually get what I want within a couple of weeks. Be careful though. I did get ripped off on a cor-20. Don't do friends and family no matter how cool they seem.