I really think you might need to rethink how it works. The largest mod I've seen for Glest had about 60 units in two factions, with very large textures and detailed models, but caused Glest to overload. If you keep the texture size small, the numbers won't make such a difference, but a large number of textures could be problematic. If you go with your 147+ units, you'll definitely want to consider sharing textures between them (have the models all in the same folder, and the models only vary in basic ways, namely the shapes in the models and using "optional" parts in the texture).
However, don't you think your mod might be a touch large, for Glest's style of gameplay? 7 subclasses and 3 upgrade paths is quite a lot of micromanagement. Plus the heros, buildings, etc.