How much to lift and when to stop?

[tallgeese]

If you're concerned with grip strength you can also work on rope climbs and do it in sets of 5-15 depending on how long of length you can get ahold of. Also, pulling an object hand over hand is useful as well. I've used a milk crate with weights but you could tie a rope off to anything. Again, this works grip very well.

As for the wrist curls and such, start off with high reps, say 15-20 for 3-5 sets. That's going to be more useful for most ms-ist than heavy weight and low reps. You can very your training once you start to see results.

Don't forget you can also lever stuff in you hand. For instance, find an old sledge and just work on lifting it from a horizontal plain to a vertical one.