Everything on a bike works together. Anything that you change usually affects something else.
There's tinkerers and there's riders:
If you're the kind of person who likes to tinker with your bike, go the upgrade route. It will probably put you on an endless process of changing out one part after another to get the combination right but that's what us tinkerers do. If you ever finish, you'll have the satisfaction of owning a one of a kind bike that you personally designed.
If all you want to do is ride, you'll almost surely find happiness quicker with a new bike. Every single part brand new, every part designed to work with every other part and a new bike warranty.
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My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.