I'm really glad this worked out! I was just going to chime in. I definitely can't speak to all the nuanced knowledge of what parts can work with other parts for which they were not originally designed or how to get by with buying the least amount of parts needed to get a bike functionally upgraded (such as moving a vintage bike to brifters without replacing the entire drivetrain). But I also don't have the taste for hacking together parts from separate brands and lines. Call it OCD or laziness. I'm not sure which. I tend to try to do all my builds with a single groupset (same brand, same or close to same line). It was all designed to work together and provided you are selecting the right group, it works famously.

And my input on this matter is just as you experienced. If you have the time, with patience, a solid, modern groupset with brifters can be had at very reasonable prices. Even on eBay. My recent builds used Tiagra 9-speed, Ultegra 9-speed, and Shimano 105. I got each of these for $150, $230, and $99 respectively. Each came with everything (fd, rd, crankset, bb, chain, cassette, brakes) and a couple even had the cable stops and cables and housing (hardly used) with them, and other bits. I prefer this approach partly because the end product comes out very cohesive visually, and partly because the compatibility is a given.

So, while I know things can be done and for much less money, for me, the end result and ease of installation (sans-hacks) is worth the extra money. I have also found people respond stronger to builds that maintain this cohesive drivetrain (it looks less franken-bike maybe?) so resale is a bit better too.