I would make sure I fully understood what my goals are. Dont try and mix different environments in one tank or system. If you want SPS to thrive, you have to gear your entire set up towards that. If you want LPS, then you would need to go a slightly different direction as far as flow and nutrient control.
I took me the entire last year to upgrade my system. Now that it is done, the only thing that I second guess myself on is the returns coming over the back of the tank instead of through the back wall. Everything was very well thought out, from the plumbing, to controls, to fail safe's and seperate circuits.
buy quality equipment the first time. You cant afford to have cheap equipment fail, take out all your corals, then buy the right equipment a second time around.