Character Card Deck effects

Question. I have a viper (193) and a striker/thunder breaker (120). Do I only get 1.04x or do i get 1.0712x (stacking 1.04x and 1.03x)?

Neither. The bonus is probably be Viper (4) + TB (3) = 7 * Character Level, added to your range. Where Character Level is the character you're playing on. I haven't tested this though, so it might just be the highest, but I'm assuming it would stack just like Paly cards do.

One question i failed to find an answer to,

Can i have 2 of the same decks? Theoretically, if i would make 6 pirates to get the 8% pdr effect from having 3 pirates on both my decks, would that stack? And i assume that by using a card in deck 1 i disqualify the card from being used in deck 2, correct?

One question i failed to find an answer to,

Can i have 2 of the same decks? Theoretically, if i would make 6 pirates to get the 8% pdr effect from having 3 pirates on both my decks, would that stack? And i assume that by using a card in deck 1 i disqualify the card from being used in deck 2, correct?

Yes, and yes.