No condescension meant. They were just factual answers.
You are of course certainly free to write a font manager if you wish, but for less than $100, you could save yourself the weeks of work writing and debugging an app you can obtain online in minutes. I would imagine that much of your time is worth more than $100?
As a self training and experimentation project, it could still be fun. As you said, it's up to you. But as I noted, why waste your time when there are already long standing apps which already do what you want? If you hope to undercut their prices as a commercial or shareware product, then best wishes to you.
Cheapest price I found for Suitcase Fusion 5 was directly from Extensis for $99.95. Couldn't even guess why Amazon would be charging $111 for the same full version item. FontExplorerX Pro for Mac is $89.
If you do try Suitcase or FEX, do note that the defaults are to store the fonts you add to their interfaces in a file vault. I see no point to that at all. In Suitcase, I set the preference to activate fonts "In place". Which means (as I would guess you aware) that they are activated from any folder or drive the fonts are on. They don't need to be in any specific place at all. You can make any number of sets you want to activate fonts for the project you are doing at the time. Deactivate them when you're done.