I think buying a new fish tank should take a lot of things into consideration...
1. If you're planning to keep SPS, you'll want a tank that's not too deep or you'll spend a fortune on lighting and a huge chiller.
2. Unless the room is designated as the "tank room", putting a 300 gallon tank in a 9x14 room won't allow for much of anything else to be done with it.
3. I must agree... bowfronts or corner tanks are probably not a good idea for all the reasons listed above.
4. Insure that when you buy the tank, you also have enough money for the sump, the best lighting money can afford, pumps, etc. Ain't nothin' worse than having a hobby you can't afford to enjoy fully. A smaller, well equipped tank will be far more fun than a larger one you can't afford to equip and maintain.
5. Tanks over 90 gallons usually require a chiller. Put $600 in your plan if you want a large tank.
6. The bigger the tank, the more water you'll have to change and the more top off water will have to be added due to humidity in the winter months here in Houston. I'm stating the obvious, but if you don't have a RO/DI unit, you won't believe how much this helps with water changes and addition... budget $80 for one if you don't have one. ReefSafe Canada has them on Ebay for less than half of local retailers.
I hope this helps! I was given a very nice 150 gallon setup with good lighting, a chiller and large pumps... but I didn't count the costs of maintaining it, let alone filling it up with critters. Wish I'd had someone sit me down who knew all it would cost so I could have saved up the money to do it right instead of upgrading everything, which has been far, far more expensive.