Hi Malena. It's good to see someone having a crack at getting an Ultima server going again. I just saw your project on Massively Overpowered and thought I'd check it out.
While Britannia Reborn was set in a different period from UO (many generations after the Armageddon of Ultima IX) and has some slight changes to some islands, if your interested, I still have the original maps used to generate Britannia in WU.
The landscape was originally taken from the UO map and them modeled using World Engine so it could be realised as a fully realised world sized map. I was way too ambitious, trying to do it as a 16k map, but it was a lot of fun creating it anyway.
The lag issues I had were, I believe, because of the map size during the earlier stages of WU. A lot of people warned me a map that size coyld have problems, but I tried pushing the boundaries anyway. Latency issues were because I had to host it at home ... because a commercial server of that size would have cost way too much to run and it needed a very beefy server (32Gb RAM minimum). I'm not sure if 16k maps are better supported, but I'm sure the WU folks have the fog spider bug licked by now.
With some work, the map could be scaled back to 8k and could possibly retain its original feel. If you wanted it to be more precisely reflecting UO itself, the map would need some rework. It's extremely close to the original Britannia though.
Let me know if you're interested anyway.