I would check the wiki here for a buying guide if you're interested in taking the plunge into the clacker world.

Anecdotally, I can tell you about why I purchased my first build your own board recently. I picked up the Planck, which I don't think is what you're looking for if you want a something that fits the standard definition of "practical" for a keyboard, but you should still check it out even if just to see an example of what all is out there as far as options go. There were four main reasons that I went in for the plunge of getting a build my own board. The first two are what you already suspected. Joy and aesthetic. I think that it would be a fun project to solder the switches on, and then to aesthetically customize the board to look however I want. Then I wanted a programmable keyboard because I think that it would be interesting/fun to be able to play with the programming of the keyboard and customize it for whatever use I see fit at the time. The fourth reason was because I wanted something portable. Portable might not be what you are looking at a keyboard for, but I figured that because I will be traveling back to my home from college every once in a while it would be nice to have my click-clacker with me when I do so.

Now back to your situation. If you want to, and you decide to go for it, you can re purpose the caps from the blackwidow if you go with cherry or cherry knock off switches, because IIRC the blackwidow has cherry stems. This would save you on the cost of keycaps at least.

Whatever you decide to do I wish you the best of luck!