[Ms_P]

I'll answer #3.

If you really think your going to get more than 1, if possible it would be safer to get them both at the same time. I say safer because if they are the same age and used to being with each other there will be no adjustment, like Kemo's Mama is going through.

I was lucky, I got my second chi, Koke, when my first chi, Sandy, was 6 months old and they loved each other from the start.

 

[Ms_P]

I would not leave the bigger dog alone with the chis until you are absolutly certain that nothing is going to wrong and the bigger one is not going to harm the chis.
You are only going to be able to tell this from observation, so it's going to take a while.
I have 4 cats along with the 2 chis, and I always seperate them when I go out.