I turned my 125g cichlid tank into a reef a year and half ago. I just finished upgrading it to a 280g a couple weeks ago as it was already getting full. Also with a center overflow aquascaping would be tough, and corals do grow faster than you might expect. I love tangs and some of the bigger fish and with a 45g you would be limited to the type and number of fish suitable for that tank. As you mentioned it would suck to drop a bunch of money then be wanting to upgrade in the near future. This hobby is VERY addicting so be careful.
