-Are there benefits to fishing in Felucca instead of Trammel?
Not that i know of!
-I noticed a "High Seas?" expansion. New boats, new monsters, new fish etc. Do we have anything like that here?
Some of the deco was made available through donations or from ed's, for the boats, a few big boats can be found in the world but for now have no purpose that i know of!
-Do we have BoD books?
Yes, the ultimate bod book, reagent, stone, ingot, tailor and many more keys can be found on the red stone in Trinsic.
-I've done a few maps in Trammel but not Felucca yet. Will I only get arti's in Felucca?
I have completed maps from both facets and got arties from each ones, also, we have themed maps here, greater loot but greater mobs to fight!
-Thieves guild. I want to join to steal arti's in Doom. Will there be any detriment to my character for joining?
No need to join a thieves guild to steal arties in Doom, like the Nike logo used to say; JUST DO IT!
-No 3D support correct? I've never tried UO in the new UI.
I believe you can play 3D but you wont see any of the custom content of the shard so better off playing 2D.
Enjoy and have fun!