I am not sure exactly what the limit is on vertices .... but (IIRC) the "limit" on a single object is around 8,000
faces ... (maybe one of the Dev's could provide a more accurate answer).
(Like most 3D games) the "art" is in making
low polygon models with high
texture detail.
This basically means that your models should be quite basic in shape, and then the "detail" should be done with the tetxure.
This is a "basic" principle for most 3D games, including (if not especially) Uru, and often one that people get wrong at the start of Age building.
You do
NOT need to make highly detailed (and consequently high polygon/vertices) models for things to look great in game. Not only is it unnecessary, but (obviously) the more polygons an Age has, the more strain this puts on the game engine, your processor and graphics card ... and you (and your audience) will start to experience problems trying to play the Age.
Probably the largest of your models (we call them objects) will be your landscape... especially if you are designing a (physically) large Age. You can always split your landscape object into smaller pieces (maximum approx 8000
FACES) to ensure an export.
To give you some idea of how low polygon Uru really is, (IIRC) Relto has about 100,000 polygons (in TOTAL). That includes
everything... all the small details are mostly done with textures, not models.
Now, if you are making objects with 5,000 polygons each, that would mean you could put only 20 "things" into an Age the size of Relto ( and that includes the landscape!)... so now you are begining to get an idea of just HOW low poly you need to go.
You can see therefore, that the lower polygon you can make each object, the more objects you can have in an Age before you start to stress the game Engine & your (and other players')graphics card... so, the simple rule when making models for your Age is to ask yourself these question BEFORE making the model:
1) what is the BASIC shape of this object
2) What detail can be done
with a texture rather than the actual model's polygons.
One of the most commonly used "tricks" when trying to add detail to models is to use textures with
transparency ... that can save you thousands of polygons/vertices in an Age ...
so, the simple rule: make your models as LOW polygon (and consequently vertices) as possible
Good Luck !

when it comes to Age creation ... "DOH" seems to be my middle name...