First let me tell you that I am not a breeder. I thought others would chime in but I was wrong. I will give you my opinion and my experience here.

I have seen here where males bred fine at 500 grams and a few times even smaller. The important thing is to keep a close eye on him. Males will breed to death. If you notice much weight loss I would pull him out and I also would not try to breed multiple females. I would do one and done if at all at the moment. IMHO.

I'm just curious.
What's the hurry that makes you want to breed now?
Are you going to buy a female and what is the plan there?