Yep, I hit the limit on both but not sure what it is. You can add a fair few new ones though and probably best to add new ones rather than replace ones for your mod. I used DJs tutorial on adding new units in guides section. You add new entries in:
data\export_descr_units_enums.txt
data\text\export_units.txt
data\descr_model_battle.txt
data\export_descr_unit.txt
data\descr_mount.txt (an entry must be put in here as well as model_battle for new mounts)
data\models\unit_model.cas (model export)
data\models_unit\textures\unit_skin.tga.dds (texture)
data\models_unit\textures\unit_skin_gloss.tga.dds (i don't bother with this normally)
data\sprites\unit_sprite_###.tga.dds (i normally use an existing one)
data\sprites\unit_sprite_###.spr (i normally use an existing one)
data\ui\units\faction\#unit.tga
data\ui\unit_info\faction\unit.tga
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