Can I play Blue's Tactics if I have more than 8 cards in my hand?
Yes, because you could still have less than 8 cards in your hand by the end of your turn.
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01)
If I use Blue's Tactics and then later KO an opponent's Pokemon, do I take prize cards and then draw until I have 8 or can I choose the order this happens in?
You take your Prize cards first, and then at the end of your turn you draw for Blue's Tactics.
Source: TPCi Rules Team (2019-08-01)