My take is: it's important to have a great amplification to speaker foundation. And sources become increasingly more important after that, the right foundation of amp and speakers will show you so much that is wonderful--and not so wonderful--in source components. After that it's fine tuning. Clean electric, isolation control, cabling--all became important to me once I got the amp-speaker and component foundation selected and perfected.

Percentage. . . there are so many variables (new, used, vintage, SOTA and combinations etc.) that I won't throw out numbers.

To a new listener/enthusiast an important question or three is/are: tube or solid state, vintage or new production, digital or analog or both, and perhaps patient or impatient.

Also: what music one predominantly will listen to will influence choices. I'd like to say that a great system will treat any genre with equivalent excellence, but in the world of practical selection and daily use a system that has one dancing and head banging to rock or other amplified material is one that may not showcase classical, folk or jazz etc. in the best light, and vice versa. (Just my experience, I'm beginning to realize this more as time passes). Keeping in mind what will go in and come out of the system can help pinpoint the system one wants and needs.