http://www.gigabyte.com/products/product-page.aspx?pid=4668#sp
Based on the above specifications you have 4 sata connectors so you can install up to 4 total. I'm guessing with your 2 hdd and 1 dvd drive using 3/4 sata connections you can now then only add 1 more. I've never heard of your psu but based on the 550W rating if it holds true then it should be more than fine.
Based on this list:
http://www.tomshardware.com/answers/id-1804779/power-supply-unit-tier-list.html
Your psu is un-tiered. It is preferred that you pursue as close to tier 1 as you can afford to ensure reliability of power delivery. Going cheap with the psu makes decisions like these more questionable than it otherwise would be. This acknowledged, it shouldn't mathematically be a problem. However, brand, reliability of components from an un-tiered psu I cannot make you any guarantees but simply put in theory it should be just fine.