I looked into this in depth a few years ago. I wish that, I still had my notes. Let's see what I remember...
I don't remember the election event line going anywhere, so that may be new.
If Hungary wins the civil war, then rump Austria will get an event chain about civil disorder (Triggered by the HUN victory event), which gives either a Red government or a military government.
The military government will ask to join Germany 50%(+?) of the time.
For the Red government you are given the option the send the German Army to restore order. This makes Austria a puppet and leads to union. It will also lead to a diplomatic crisis with France, but if you play hard-ball on each event they will back down short of war 95+% of the time.
As for Bohemia, there is an event if you control certain provinces that gives you cores to the Sudetenland, no badboy or dissent.
I don't remember anyway to get cores on the rest.
I don't think there is any way to annex them without war - barring some really weird ACW outcomes.
As for improving your chances, I think there is only the EU2 way.
I am having trouble remembering this for sure. But there events preventing your shooting involvement in the ACW. I remember having a alliance with Poland getting me in on the Hungarian side once.
You guys are tempting me to reinstall KR....
