Louisa is a family name for me so I love it's antique charm and literary connection. Because it ends in an "a", I would avoid mn's beginning with a vowel (eg. Louisa Olive, Louisa Eleanor). I like one or two syllable mn's with Louisa myself.
I'm not a fan of Louise/Louisa (might be the 'wheeze' sound in there) but I can understand why others might like it a lot.
Louisa Mayfair (I LOVE this!)