with good 'seeing conditions' and with a 150mm Dobsonian telescope, how many of the moons of Saturn could I expect to see?

You may have a chance to see Titan, the largest Moon in the Solar System. But you will need a good eyepiece and a good dark location with transparency and steadiness.

Tethys, Dione, Rhea and Iapetus are possibilities as well but they are not easy objects.

One trick that can help is an occulting disc to block out Saturn. This can work wonders spotting moons as well as faint companions in double stars.

None. I once observed Jupiter through a 250mm telescope in an observatory, and saw only the four largest moons of Jupiter. Saturn is much farther away, which means it and it's moons are dimmer, plus Saturn's moons are smaller than Jupiter's. You have no chance of seeing Saturn's moons.

It depends on you - I've never seen more than 2 (with a bigger 'scope), but I know someone who can see 7!

I think you might see Titan... I doubt you'd see any of the others.

If conditions were perfect you might see Titan. But none of the others.

You could see all 4 Galilean moons of Jupiter.

Titan, plus probably Rhea and Dione. Maybe Tethys

I would say two when visible.

What Dobsonian scopes I have seen have some decent optics, more bang for the buck they say.