I'm not aware of any 'custom ROMS' that are available for WP7 devices, since the various bottom layers have not yet been cracked, as far as I know.
That said, I'm not sure that the device is at fault, and definitely not the O/S. There are plenty of us around using the Focus (it was one of THE most popular WP7 devices ever) with no problems -- certainly not the ones you are experiencing.
Your signature/profile don't say where you are or which provider you are using -- but many of the problems you describe could be due to problems at the service provider end, not the device itself. Obviously it is frustrating when the phone does these things, but I'm not sure there is a quick fix available here for you.
BTW, this forum is for the Focus S -- there's a separate one for the original Focus unit.
Device: HTC 8X