Professional fit is the best advice you can get & money well spent if you are going to plunk down a good chunk of money. A good shop will do this & maybe even throw part or all of it Into the sale of a bicycle. Why throw your money at a moving target?
understanding fit can be tricky & every geometry has its special "qualities". Unless you are deeply steeped into bicycle geometry & are willing to pull out the paper & protractors, I say work with a good local fit expert