Just chiming in... I'd say you're over complicating your UI by having so many individual target macros. I feel like you're working much harder than you need to in order to play efficiently!

I would scaling way back on the amount of macros and just get better at switching targets mid-cast. Like somebody mentioned, there's plenty of time during cast/gcd to switch. It'll just take some getting used to, but when you do you'll be able to sip your coffee while healing! xD