I'm from Malaysia, though it's embarrassing for me to say that I'm not knowledgeable about the laws here. What I can say is that Malays are legally bound to be Muslims by the constitution.

I'll try to address some of your concerns:

I gather that my friend cannot talk about this to local friends or family in Malaysia because those questions would be "insulting to God".

Malaysia is an Islamic echo-chamber. Although critical thinking is gaining a foothold here, but it is not valid for questioning religion. Yup, your friend will definitely be in trouble if he mentions his doubt to his friends and family. They'll say to him that he's being manipulated by the Western devils and should reaffirm his faith by getting closer to Allah. People here just can't stand the thought that their beliefs can be challenged because for them, Islam is the absolute truth and no amount of questioning can change them.

Heck, we even have the Islamic equivalent of the American Idol, where people compete to become the best Imam. Islam is deeply ingrained in our culture and I don't see it changing anytime soon.

However, I would love any inside views of Islam specifically as practised in Malaysia, particularly the role of the family, women, children, and working life.

We're not that different than any other countries. The current ruling party is quite liberal despite the constant pressure from the opposition that a stricter Islamic law should be imposed.

Also, I have some basic security questions: can my friend get in trouble for receiving internet messages that might be "insulting to God"? Can they get in trouble for sending emails that are questioning of basic tenets of faith? Will they possibly get caught (i.e. do the police seek out this kind of thing)?

Not that I know of. There's no one monitoring your emails or anything. As long as he doesn't make his views public, he'll be fine. The 'religious police' will only nab those who commit pre-marital sex, prostitution, and eating on the month of Ramadan.