Advice needed, should I get a 3rd dog?

I'll start by saying that there's just one of me, no spouse/kids/etc to help out. I've currently got two miniature Australian shepherds (Ellie age 3 and Fletcher age 2). The rescue I got them from now has two 6 month old mini Aussie puppies and I'm very tempted to get one of them. I just worry that I'd be getting in over my head taking on 3 dogs instead of the two (no issues with the two--I find them quite manageable). I understand the financial implications of adding another dog and the whole thing of course would be dependent on the three dogs getting along with each other, but beyond that I wonder if I'm crazy to think about a 3rd? I'd love to hear what everyone else thinks!