Just got my first thinkpad. Has anyone tried El Capitan on the x220?

Realized I could do this after seeing this page. I'm currently developing the iOS version of my game in a VM, which is horrendous, so this seems like a pretty good way to get around the the $1000 xcode paywall of having to own an Apple machine. My questions are:

1. Is it relatively stable? How often are the kexts hosed by system updates?

2. Is it possible to easily dual boot Win10 or a GNU/Linux distro on the same drive as the OSX installation? I could pick up another SSD but IIRC the msata port is only 3 Gbps.

3. What's the risk involved in flashing the custom bios? I'm not too scared of it but would prefer not to brick my brand-new-to-me x220.

4. I also got a StarTech USB 3.0 express card because my x220 is an i5. Will that work in the OSX installation?

I think that's about it. P.S. super excited about joining the Thinkpad club!