Any pitfalls to shutting off house water supply while working?
In general, there's no problem using the main valve. However, if the sink valves are stuck, you might find that the main is also in poor repair.  If the main is old and rarely used, you might find that's it's stuck or will become stuck once closed.

If the main valve is a gate/globe valve, and it looks old and cruddy. You might want to consider replacing that valve as well.  I'd recommend replacing it with a ball valve.