I'm not sure how the shift key will help with micro, you still have to manually queue everything up and if that engineer gets destroyed you have to start all over again
And I am aware of the attack move, but I read that spamming attack move can bugger up the pathfinding. I have noticed that the pros use patrol as well, I guess for this reason. I still think my approach of focusing on the main part of the map then switching to the islands when you are at a stalemate/advantage is valid.
Edit: Also, when I gain the advantage I have no trouble telling what to do because things naturally happen, for instance the mass meter begins to fill up, you realise you have to upgrade mexes, etc, you realise you need to tech up for a final push, but when I am "on the ropes" so to speak I find it very difficult to think how to proceed.