I never played an old bugged version of Outcast unfortunately (?), which is why I can't do any direct comparisons. But I was able to complete every task you mentioned. Lighthouse was lit and I think I completely stopped food production by convincing the people to stop giving different kinds of food (riz, fish and something else I think...) to the soldiers.
Mud-walking and twon-ha-riding had been a blast either! :D

So I think you should be good to go!

The GOG version has fixed all processor speed issues, but be advised that you wlil only be able to walk while in the riss fields, not run. This was because the author of the fan fix that fixed the processor speed problems set it up that way. In the original, unmodded version you could run in the riss fields, provided you didn't run into processor problems.

I was able to light the Cyana lighthouse in the old unmodded version, although it was a little tricky. There's a thread about how to manage doing it here:

http://www.gog.com/forum/outcast/cyana_boat_light_solution_no_patch

I didn't have the patience either so I just used a CPUkiller to help me out. People talk about ways to get around it but honestly, just slow it down, hop around, and keep going.

I played the original 2 CDs French distribution years ago when it was released, and did finish it without meeting any major bug.