I have similar interests as well! I can't really help too much but I'm glad you started this conversation.
I read in a Barista magazine once tips for exercises and it seemed to have self care tips for Barista's as well. I haven't been able to find that particular magazine since, but a little online research could probably dig it up. What I do to not to let customers get me down is to try and teach each customer a little tidbit about coffee every day, and doing so I learn more myself.
Definitely get feedback on drinks and customer service by talking with customers. Its a good way not to let yourself get to caught up in "snooty" attitudes that sometimes come when customers don't know how to order drinks properly.
And days off are DAYS OFF.
Garlic Pills. Yes I know it sounds crazy and weird. But i swear they work. Get the odourless ones. Remember that caffeine effects your adrenal gland. This realises adrenalin as well as dopamene. Being a dominant hormone your body is forced into fight or flight mode. you will then get the stomach cramps ect from the caffeine. Garlic counters the effects of adrenalin, thus helping with the stomach and jitters. As well as stick to espressi. The milk in a cappa is what keep the caffeine in your system for longer.