1. Please re-check the availability in all your regions with the market buildings.
2. The unit size is from vanilla and I didn't touch the related "unit_stats_land" table.
3. I made them only recruitable in the pirate buildings because it would fit best. But you're right that these buildings are very rare on the map and the player has to control lots of regions before he can recruit them. I could make them available at the market buildings too. In a sense of mercenaries.
I can create new custom units after the "units" and "unit_stats_land" tables are accessible.