Depending on the type of music you play, you could be averaging 200k-500k points per song, so you'll have to play through a few thousand of them. It's gonna take a while.
But there are ways to speed up the process somewhat. Knowing how to maximize getting points in a song could easily chop off a few hundred hours from the process.
DON'T HIT EVERY BLOCK IN THE SONG. In fact, you end up avoiding a lot of blocks in order to get higher scores. Prioritize getting a fuller match over picking up more notes.
For reference, having two full lanes (14 blocks) is worth less than 7000 points, but three full lanes (21 blocks) is worth more than 15000 points! That's more than twice the amount of points for picking up 7 extra blocks. This makes an especially large difference at the power blocks.
The power blocks are the 'loops' during the song. DON'T IGNORE THESE as they're worth more than anything else in the song. If you have to decide between finishing a match or extending it so you can hit the pb with a full grid, hold the match!
And don't forget to use spikes to your advantage. There's no 'stealth' bonus here, so if you accidentally fill the grid up too early to reach a pb, you can hit a spike and extend the timer.
There's plenty of other things that can bump up your score, but you'll do fine enough with that general advice.
When it comes to music choice for points, louder+more percussion+more noise = more blocks.
Most metal from the 90s onward is worth a lot of points as long as you stay away from the 'slow atmospheric' stuff. Black metal will have the most blocks.
There's plenty of electronic music that will get you a lot of points. Mainly EDM. Trance and drum n bass will give you lots of blocks on average, but you'll also do fine with techno, eurobeat, any rhythm game music...
As for rock, it depends on the style. As usual, the more noise, and the faster the music, the better. Most punk rock works great (pop punk included), plus there are a lot of noisy underground rock bands (most music tagged as 'shoegaze' is great for this).
Hip hop can have a good points per minute ratio depending on the style. Trap hi-hats generate a lot of notes, and loud old-school beats work, as well.
Experiment around and see what works.