Your options are limited to some sort of freehub fixing device such the old Surly Fixxer.

SPNKwheels

You are unlikely to find a wheel with fixed threading or a bolt on cog that fits that frame and also has a disc brake rotor mount.

As far as installing a suspension fork on that frame, most probably it can be done, but a better question is why would you want to ride a fixed gear if the the roads are that rough.