My husband converted to muslim

If he becomes a muslim, he is allowed under shariah' court to take 4 wives; with certain conditions as provided by law;

Local law comes first as far as your government cares.
Find out what that position is and you have your answer.

4 wives is fine, but consider he may not enjoy the nagging.

I think you should rather talk to him about your worries and about if he has legalize it. Personally i never knew you had to legalize religion. I never got anything from  a christian priest to show am christian. Maybe a certificate for baptism and first Communion but never any thing from that.

What i am trying to cut across is. Whether legalize or not it highly depends on what he believes in and on the religion he has set his heart on. If he reads and complies to the Quran, pray 5 times daily i think you won't need a paper to prove it.  Talk to him.

Just my personal opinion:

If I were single, and a guy asked me out on a date and I learned that he's married, I'd be turned off instantly and would never go out with him again. And I think many women would react the same.

But if the guy had irresistibly good looks, a hot body, lots of charm and a ton of money,  some women might think it over. (Maybe just a ton of money would be enough for some women.) Does your husband have those qualities? Do you think women will be turned off, or will they be lining up to your doorstep?

There seems to be a little misunderstanding going on here.

1 - Some people convert to Islam for personal gain of some sort.
There was a thread on here a few days ago where the OP admitted he'd converted to make it easier to get a job. Some do it for marriage (one only), but never intend to be a Muslim.

2 - No legalisation is required. Whist many places give a certificate or ID card, once a man makes the declaration of faith in front of two Muslim men, he's a Muslim - full stop. This is the part that makes me laugh about George Galloway; he continues to claim he's a Catholic, but he's gone through at least two Muslim weddings, and that involves saying the declaration in front of two men. As far as Islam is concerned, he's a Muslim.

3 - A Muslim can take four wives in Islamic law, but local law might well stop him doing so.

4 - Because someone can do something doesn't mean they will.

Popular newspaper rubbish makes it sound as if "Muslims: all run around after or buy four 13 year old wives, but this is total fabrication. A few do, but in a very few places in the world, almost always in poorer countries where the education system hardly exists and/or the form of Islam in that place is very strict.