Yes you should change practice minutes. Some coaches say go with 15/10, so 15 in FB/Press and 10 in Motion/Man, but I prefer going a full 25 or even 30 practice minutes in your new system to get players learning it so next season your returning vets will be competent. Take the losses this year for future gains, if not, then do the 15/10 method.
Hopefully some of those STA's will improve still, those 65/64 STA will kill you in your new system. They basically will play less then 10 minutes a game.
I would recruit ATH/SPD and STA before DEF. In a Press defense, the DEF rating helps, but the ATH/SPD is more important (slightly). I would recruit all 4 if I were you as they all are really, really important in what you're going to do.
I haven't ran a Fastbreak, but I've ran a FCP at D3. Focus on ATH/SPD/STA/DEF mostly and you'll be alright. Best of luck.