First boot up after assembling new computer?

If you have not already purchased the Corsair VS 450 I recommend changing to a tier 1 or tier 2 power supply.
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

The Corsair VS is a tier 3 model, the quality is less than good. Unless that is all you are willing to spend...

As for the case I ALWAYS say reusing a Compaq, Dell, HP, etc. case is a bad idea, ripe for problems. I'd hate to see you get all your parts and have some propriety compatibility issues.