I had the same problem with my recent addition of my "Ape Man" where each time I built the unit, it would crash the game.
Accuracy is the key when making changes to XML files. You put in the an errant "/" or a different name that is being linked to another of the XMLs and it will crash.
Also for artwork (models) I found that it is imperative that you copy very similar art logic because some models just don't like massive changes to sizes, formation, numbers of units, etc....
Also if you are creating new UNIT XML that is why you are seeing only your units. It is better to start with a pre-existing mod that you know works, and then mod from there. Remember this is a learning process so you want to start with something you know works -- no sense in recreating the wheel when there is so much available now to experiment with.
Just some ideas to keep you going --- hope everything works out.