Lots of good advice above. However, as I am cheap and like to keep things simple, I have found that I don't *need* all of it.

For me it is not so much the number of gears but the having the right ones for the job on hand that is important. I can be perfectly happy with the right 2 x 5 or 2 x 6 setup:



I have come to like brifters for touring lately, especially in the hills, and have done a couple of conversions of my favorite touring bikes by not much more than mounting a set of used brifters and "correct" (i.e. matching the shifter's cable pull and cog spacing) rear derailleur. A freewheel with ramped cogs isn't strictly necessary but improves shifting considerably. The same can be said for modern shifter cable housing.

The one that has got the biggest mileage so far is this Austro-Daimler Inter 10: Reynolds 531 frame and forks, no braze-ons, 700X28C tires and fenders, 3 x 6 indexed rear shifting:



Another cheap and cheerful route - for those interested - to to brifting pleasure is Sora 7-speed. Not as pretty as Campagnolo, but works very well. I built this parts bin special as a Covid Christmas project: