still new to keys, cards etc. some tips?

use this http://www.tf2outpost.com/ and http://forums.backpack.tf/

YES

Refined metal (tf2 metals)

Yes (most people accept both as payment)

PRobably 3 or 4 trading cards for a key

Just looking at the market would have solved all of your questions...

Relative value between TF2 keys, Dota treasure keys and trading cards can be found from the merket (cards don't all have the same value).

REF are refined metal (TF2 item)

The number of trading cards per key is very different depending on the game. For example, TF2 cards are only worth about 50 cents each. While some like Bittrip runner 2 ones are worth like $1.50