Yea. That's the only thing I disagree on if you intend to use vacuum advance.
I would work in small steps from where you are now.
I would go for 18* at 750 rpm and make sure there is enough tension on the spring to be sure its really the initial.
With a relatively rich mixure there shouldn't be a need to light it off early. I'm running 17* initial with a 230 @ 50 cam right now. heads, compresion, intake valve closuing point all have some effect so no one answer.
Don't worry about where the idle mix screws end up. That's what they are for. As long as they have effect. If you turn them and there is no response, then they are out of working range. Four corner idle is going to be more difficult. Try not to have to mess with the secondary IFR and IAB as that will impact how well the secondary opening responds.