I will probably be getting a Yamaha FG750S, but I would like to know, what strings do they come with and what guage?

Also, what strings do you recommend for this guitar, if I am playing all sorts of styles - Strumming, fingerpicking etc...

This might not be helpful at all but I have a Yamaha F310 and it has light gauge FG12 "folk guitar strings". String gauges are .012, .016, .025, .032, .042, and .052. I'm pretty sure they use these on all their guitars I'm not completely sure though.
Yamaha F310 acoustic
Ibanez RGR321ex
Peavey Vypyr 30
the question may not be relevant if you're buying in store. often the strings are changed by store employees after the guitar has been there a while.

what kind of strings you use depends on your personal preferences regarding playability and sound. my husband and i both play extra lights - usually phosphor bronze. i strum and fingerpick, and find lighter strings are easier to play, although depending on the guitar, how you play and the strings, you may get more volume and tone with heavier strings. i get great tone with extra lights - 10s - although i find any lighter strings to be annoying to play.