Not familiar with "Think Different"...anywhere I can check it out? Auto or photo? Also never used AN nutes so can't be much help there but sure there are plenty here who can...
600W should be fine, what's your room dimensions? 5 gal should be fine depending on veg time...
OK just checked out "Think Different"...you can tell I'm new here. lol But not new to growing...so yeah, 5 gal should be more than enough.