1. You can build nomadism in provinces with a nomadism or a mixed hidden resource, pastoralism in regions with mixed HR or without HR and Client Kingdom everywhere else. Nomadism has a weak economy, but lots of cheap HAs, pastoralism has more infantry units, less cheap HAs and a slightly better economy. CK is basically a Lvl. 4 gouverment.

2. You can't build CKs in the greek cities on the bosphorus and thus you can't recruit Bosp. Heavy Archers (not like you'd need them anyway),unless you leave the Greek lvl. 4 gov. in place. (Cheating, kind of)

3. No reforms AFAIK.

4. Do what you want. The Hai aren't really a problem, neither are the Getai.

5. No clue.