I have Scott Cook heads and intake, he recommended starting with 28 degrees total timing. My last engine dyno run made more power at 24 degrees total and I run 15 degrees at idle but my camshaft and comp ratio is a lot higher than yours. My engine idled at 900 rpm, also run with 8 degrees vac advance unported.
I also get 8 - 10 inches of vacuum at idle but I have never had an issue with brakes. I have had my brake servo reconditioned and run EBC RedStuff pads on the stock large later style brakes and they work great.
You will never know what is really best for your engine configuration unless you have it correctly tuned on a dyno.
Your engine running on after shutting off at 1,000 rpm is not good. Have you checked the spark plugs that you are not getting uneven fuel distribution?Running correct spark plugs, extended tip, correct heat range?