What I did was use fedifinder to find all the people I already followed on Twitter and bootstrapped my account that way. It shows you what the most common instance is among the people you follow which is a good recommendation to choose that for signup, and then you can naturally find other people to follow through their boosts.

Also you don't have to fret about what instance you start off on. I started with one of the generic instances and then after a week of lurking I migrated my account to an instance that I wanted to join (which moves over all your followers/followings but not your posts)