Built-in wifi adapter is common on ITX (HTPC oriented) boards, so you'll probably need a separate one.
Windows 8 is identical to Windows 7 in terms of usability providing that you install one of the start menu replacments, i.e. Classic Shell
, it's just more feature rich.
Edit: There are very few compatibility issues that can be avoided by installing/running the problematic software in Windows 7 compatibility mode (takes 3 clicks to do it, literally).
Only truly incompatible piece of software I encountered so far on Windows 8 was Acronis Disk Director which uses driver module that isn't Windows 8 certified, causing it to not work.
On the flip side, I've encountered quite a number of old games that work perfectly on 8 that had various issues on 7.