[G&K] I took over a holy city.

Any benefits?

I do not have a religion (only 40 faith total right now), but do have a Pantheon.

When I auto-spawn my first great prophet at 200 faith or whatever it is, will I be forced to found my own religion? Can I found it in the same city as Islam (the religion I took over) for fun?

Can I just totally steal Islam? All my cities are already Islam anyway and Islamic Egypt had done a huge religious focus and spread it across half the map before they foolishly attacked me and lost their capital (7 wonders!). I don't even care about the Founder's bonus... I just want the city-state bonus, which, you apparently don't get even if you take over the religion's holy city...

Any way to really adopt Islam?

This is the first game I played with absolutely no thought to religion, so I'm a bit lost as to what this all means.