So from what I can tell, would I be better suited (with beginner level experience) getting an older, vintage 360 and putting the magnum heads on it as I had considered doing with the 318?
Not really. The only real difference parts wise is going to be the valve gear. The lifters, pushrods, and the difference between pedestal and rail mounted rockers. The later vintage 318/360 uses a roller cam like the Magnum does.
Most vintage engines use a flat tappet. The AMC V-8 lifter can be used with tubular pushrods to provide lubrication to the top end of Magnum heads.
I know there will be a special intake and push rods that allow oil to pass through (and a few other small modifications). Would a vintage 360 be an easier rebuild and install for a novice?
I don't think the older LA is going to be any more difficult than the Magnum. Aftermarket support of the Magnum is going to be less than the "vintage" engine.
With the vintage motors I can still use the older LA flexplates and balancer? Would I need a different converter than what my 318 uses?
The older 318 is internally balanced. The 360, vintage or Magnum, is externally balanced under normal circumstances. So yes, a different converter is required.