As mentioned above, you can do up to 120 credits per year in agreement with student services and module teams. I know several peeps who have done 4 modules a year, though I'd caution against overloading yourself if you don't need to.
I did 3 stage 3 30 credit modules in a year recently and it was probably one too many for my work/social/study balance and properly burned me out. That's just me though and I wasn't as prepared as I'd have liked to be.
Just make the decision that's best for you and your situation at the time. I had credit transfer from a lower qualification and skipped 3 modules, so I'll be finishing my MEng in 2 years time, coming in at about 8 years rather than 9.
Welcome to the OU community, it really is a wonderful place with brilliant people. Enjoy your university adventure and best of luck. 😀