No, the cards are random but u do get to choose which clans to choose from. Different packs come with different clans etc. The cards u usually get are Rare+Uncommon+Common or Uncomm +2 Commons. In the 20 credits packs, the rare card isn't garanted but its gerenally better than the full deck cause the cards u get are alot more concentrated clan wise so u might get the cards that u will actually use. The full deck does give u 1 rare card for sure but since u haven't bought any credits. go for the smaller packs.
No you can either get a pack for 20 credits with 3 cards in it and there are 5 of these which if you hover with your mouse over them it will tell you which set it radomly picks from. Or with 50 credits you can get 8 radom cards guarenteed 1 rare i would go with the 8 card booster that is what i did yesterday and i got some really nice cards.