Well, most guys are going to tell you are too young... wait until the 25yrs old range. Your body is producing enough natural test now, plus there is a good chance your growth plates are still open (if your growth plates are still open, steroids can close them prematurely and stunt your growth). There is also a chance you could damage your natural test production...
If you want to take a chance and screw your body up, it's your decision... Spend some time on the board and enlighten yourself. Around the age of 25, your natural test drops, so Anabolic Androgenic Steroids (AAS) makes since - but get your test levels check at the doc before you start. Eat and train until you are close to mid-20s, then juice, if you still think you need to. I've been on this particular board for 5 years, and I guarantee that no one who knows their stuff is going to recommend steroids (not even prohormones) to you at this time in your life. Be patient... it will pay off. It did for me. Also, you are a big boy already at 19 - 6'7" 295lbs... What's your body-fat percentage?
Read this post and pay attention to what is being said here and who is saying it...
http://www.steroidology.com/forum/anabolic-steroid-forum/132875-am-i-ready-gear.html - The guys giving the advice have been around a long time and know what they are talking about. Don't just take my word for it. You are playing with your hormones, so please take it seriously. There are a lot of people out there that juice at 18-19... If you want to risk it, again, that is your decision. Just remember that a lot of the advice on these boards come from professional body-builders, veterinarians, doctors, veteran users, etc... They know more than you do, so it is good idea to listen to them.
You still need to do more research... 6-OXO is not proper post cycle therapy (pct) to use with AAS. You will need something like nolvadex or clomid, and possibly Human Chorionic Gonadotropin (HCG) if you are running an extended/high-dose cycle.
Your question regarding CCs... The concentration of the test per vial/amp determines how much test you will get per CC. 1ml = 1cc. So if you have a 10ml vial of TestE 250, you will be getting 250mg of Test per ml/CC. If you want to run 500mg of Test per week, then yes, inject 1cc twice a week (e.g. Mondays & Thursdays).
Good luck.