I
Letitia as "leh-tee-sha" and personally I'm not very fond of it. I rarely like the "isha" sound in a name, I don't know why, it's just unpleasant to my ears for some reason. Though it does have a nice meaning!
Of your combos, I like all but the first...
Letitia Marianne just sounds so incongruous or something lol
Letitia Rosalind is quite nice though and the best of the three imo.
Letitia is kind of a quirky name already to me though, so I think something more "traditional" sounding for a mn (like you have already) actually fit better.
Some letters I think sound good following
Letitia, and some mixture of traditional and quirky:
Letitia VeraLetitia VereneLetitia VivienneLetitia VictoriaLetitia VioletLetitia Virginie
Letitia YaelLetitia YasmineLetitia YelenaLetitia Yeva
Letitia DamarisLetitia DanielaLetitia DaphneLetitia DawnLetitia DaviniaLetitia DelphineLetitia Diane /
DianaLetitia Doriane