T.M.
I have had several benign lumps removed from my breasts. I agree with all of your reasoning and for those same reasons decided to go for complete removal. The last two I had done were no big deal, I didn't even have to go under. Mine weren't considered to be fibroadenoma's they were more like suspicious lumps of tissue that they needed to confirm were benign, but are treated the same way as a fibroadenoma.
Don't stress too much, just get it done and over with for peace of mind!