It's difficult to do best of x matches series like this because you don't know when the result will be confirmed. We're working on adding fixed odds betting as well as the parimutuel system we have now and that will be more suited to it.
I would not suggest "freebitco" implement any sort of fixed odds betting. It's complicated business and you will need a lot of resources to maintain it. Even if you chose a good "odds provider" you will eventually have some ambiguous cases with voiding bets. If You will blindly copy paste Pinnacle lines than pro players will rip you off.
freebitco has very good reputation in cripto communit but fixed odds betting can undermine it (be careful). I would suggests you concentrate in pary-mutuel betting which you already have. But it has a lot of room for improvements. Just make it the best on the market and it will succeed.