Having a little apprehension prior to an engine start is normal (at least, it's been normal for me). Also, no matter what you plan for, be prepared for unforeseen surprises.
First question - the fuel level in the glass bowl fuel filter (at the carburetor) might go down a little, but if the bowl completely empties something is odd. Is the bowl orientated at the top or at the bottom (it should be on the bottom - post a picture of your set-up, if you can)?
Second question
- idle speed - (also see question three) do you have a new cam and a new set of lifters? If yes, follow the cam manufacturer's recommendations. Otherwise, set idle to 500-1,000 rpm.
- connect vacuum - yes, why not connect the vacuum advance during break-in?
Question(s) three - what to tinker with:
- idle - yes, set it to the speed you want (or, the speed recommended for cam break-in) - 500-1,000 rpm (as long as you have oil pressure - if you have no oil pressure, STOP the engine and ask for advice.
- vacuum - you can't tinker with this but you can watch it. If it is erratic at idle, or lower than whatever your Shop Manual suggests for good vacuum, you've got something that needs to be checked out.
- timing - sure, you could adjust this (maybe, for a start, to maximum idle speed or maximum vacuum reading while the engine is idling).
- valve clearance - this does not get re-adjusted until you have run the engine for 30 minutes after reaching a stable engine temperature. How have you set the "cold" valve clearances?
Do you know how to spin the oil pump to distribute oil throughout the engine prior to cranking the engine?
Good luck - stay cool - let us know how it goes
