Unless you have a seedbox, I’d still use a VPN on private trackers. You don’t want to expose your actual home IP address - anyone can see it when you’re torrenting (in the peers tab). You are correct that most companies that DMCA aren’t following private trackers and therefore it’s unlikely that you’d get a “love letter” but again I’d use a VPN for your home ISP.
As for getting into private trackers, there’s an OpenSignups community here. Otherwise, you have to usually know someone with invites to get in.