Are we talking full albums here or tracks and singles?

Beets, the MusicBrainz tagger can handle this.

plugins: lastgenre should load the plugin, but I think you've come that far.

In the config.yaml file you'll also need to tell the plugin to get some tags.

lastgenre:
    auto: yes
    count: 1
    source: artist

I usually keep the count at 1...

If you are importing singletons you need to use the -s option, otherwise importing albums should work.

I know that likely didn't answer the question, but somebody might find it helpful.

Ex Falso is an OK tagger for manually doing stuff.

2,500 isn't much. I think many of us here could point you in the right direction for getting loads of high quality music. But, I am not super comfortable dropping names...the first thing listed on this site is a super easy way to get started https://github.com/Shakil-Shahadat/awesome-piracy#music-downloading

Your next problem will be too much music, which is where I am at, but that isn't a complaint or a flex. It happens when you've been hoarding since the '90s.