Use or don't use vacuum advance on distributor???????????????????

You need a baseline to work from. Get ignition set first then work fuel.
Running manifold vacuum adds timing at idle. If you want 20* timing at idle you add initial mechanical and vacuum advance together. Let's say your vacuum advance can has 15* advance, you set initial to 5*. Set timing to TDC and then hook the vacuum hose up to see how much vacuum advance is in the can you have. Adjust initial accordingly to get it where you want.
Vacuum advance is built into the can and is usually marked by a number on the lever. An 11 can means 22* at the crank. The 3/32 allen adjustment changes the vacuum required to start vacuum can to move. Counter clockwise decreases advance, clockwise increases advance.
My magnum ran best ET at 34* total mechanical.
Stock cam I would start at 20* intial and 34* total 45-50* hiway cruise.
Read this thread for more info:
Vacuum advance tuning to maximize cruise MPG?