Hey, and welcome 
I am relatively new to this too, I have a 7 month old male argentine B/W Tegu named amigo, the advice that I have received here has been nothing short of awesome, so you are definitly in the right place!
In answer to your questions (and this is all from my own personal experience):
1. cage size, for young, then adult.
I originally planned to keep him in a small tank for the first few months of his life here, until I got him and realized that 16 inches is still pretty big, so we built him an enclosure which is about 3 and a half feet x 8 feet long. I know of people that have started theirs off in way smaller enclosures though.
2. temps
They need a basking lamp, with a surface temperature of around 120 degrees on one end with a cool end of about 80-90 degrees. Night time temps should be around 75 degrees
3, feeding.
Mine eats mostly adult mice at 7 months old, he likes some fruits, and we tried the SDZ diet for a while, which he seemed to like too.
4. tame.
Amigo is extremely friendly and personable, he is a bit of a wanderer, but trustworthy enough to sleep under my pillow all night, he uses his enclosure mostly to bask and to eat, other than that he hangs out in the house with me. We potty trained him in a day or two to go on a papertowel, and now he goes outside.
I hope this helps, if you make the decision to get a tegu you should check out www.agamainternational.com or www.bluetegu.com
good luck.....
Leyla & Meego x
