Absolutely yes! Additionaly booster will choose account with the closest league to yours.
No! You play DUO on your account with experienced player, that will help you win games you purchased.
Of course, you can. After getting a booster, you can determine meeting dates with him. If you cannot find any, then you will get another booster.
If you purchased "games", booster will play with you only number of games you have selected, irrespective of the result. If you purchased "guaranteed wins", every lose means one additional game for you. If your score is 6 wins and 3 losses, out of 10 games purchased, we will have to play 7 wins more..
Of course, he can. If you have an account with close rating, that you want to share with our player for DUO's time, there is no problem at all.