What does it take to get to a solid 1800 level?

Just putting in the time and commitment and doing the regular things like playing and analysis, tactics, master game study etc. I would be distrustful of someone claiming "I got to x level because I did this particular thing, or I read that particular book." If you are playing regular long games and mixing with people who are playing, talking with those and also doing some chess stuff in terms of study over a number of years then any improvement is likely to be a combination of things. However, I was probably helped the most due to studying tactics as my tactical play was probably the better part of my game.

You'd need some opening knowledge; at the very least a solid repertoire.