Where can I find these allegations of him committing sexual assault?

Probably on stallman-report.org, although I will hasten to add stallmansupport.org as a counterbalance.

Considering some others mentioned here are Elon Musk and Steve Jobs it seems like 'awful personal character' doesn't count for much.

If we completely ignore the Stallman support and take the Stallman report as completely factual and accept it at face value, then I still think the good he has done outweighs the bad.

Well, "awful personal character" SHOULD count for much in response to the question "Who is your favorite entrepreneur", actually