Well, Rhi, there is also a French Language Help thread
As kehribar said, "I don't know" would be "Je ne sais pas". In informal spoken French that could be abbreviated to "J'sais pas".
For "we'll see"... well, off the top of my head I can think of "Voyons..." which is like "Let's see...", but that may not be exactly what you're looking for...
I think my French books tend to use things like "Euh..." or "Eh..." for little pensive sort of sounds like 'hmm'. And I'm pretty sure my French friends (or one of them, at least) writes 'hum...' for 'hmm'. You can probably add more h and m's to those if you want.
It would be helpful if you could give us some more specific contextual details, especially as French has some large differences between formal and informal language and so on. You might want to go and post what you're looking for in the language thread I posted the link for, though.
OliveOil_Med - sorry, I don't know anything about French boarding schools. But I'm pretty sure your typical French school doesn't have houses, and house systems seem like a distinctly British thing to me. I'll try and find out, though.
I hope this helps you both! (I'm not French, though, so others might know better than me )