First off, I'll say that BI make wonderful pets and that whenever you feel comfortable adding one, I don't think you'll regret your decision. There's a reason why boas are as popular as they are. Boas' popularity means they aren't going anywhere, so you should be able to find the boa of your dreams whenever you're ready.
That being said... the fact that you feel like you're talking yourself out of adding a boa at this moment means something. If you're not feeling 100% enthusiastic and confident with the decision to bring on a new animal it's best to hold off. Snakes are a living, breathing, long-term commitment, and taking a new individual on isn't a decision that should be taken lightly. For what it's worth, I've been back into reptiles for roughly as long as you have and I personally can't imagine caring for 15 snakes at the moment. Yeah, they're comparatively easier to care for compared to most other pets, but they still find a way to eat up more money, space, and time than you'd anticipate. Three have certainly been enough to keep me busy!
I think another important thing to consider is that you'll likely start breeding in the relatively near future. That's a fairly demanding process in and of itself, and could very well eat into the time you'd planned on spending with your boa. I think the best thing you could do right now is hold down the fort with the snakes you already have, start setting both them and yourself up for future success, give it a season or two, and see how things go. Who knows? Maybe you'll find that your reptile priorities will have changed by then.