I like the tattoo ideas you have.. Good spots for chicks. I'll tell you though about getting them on your back.. You'll never be able to see it. Only your boyfriend and the people at the pool will be able to see it.. I have one in the middle of my upper back between my shoulders and I always forget about it unless I'm at the lake or the pool and someone comments on it...
I guess my advice is this, if it's something you're going to want to look at or see regularly you might want to avoid your back as you can only look at it with two mirrors.. kind of a pain in the ass..
I love mine though.. they all mean something to me.. that's the important part.