I'm Ash, and I'm new here.

I've been keeping a pair of male Gouldians for years. I love them dearly, but they've been in one of those 18x18x30" Petco cages forever, and I have the opportunity now to expand to something bigger. There's a Prevue F030, brand new, on my local Craigslist for a pretty good price.
Here's my question. I'd like to have more birds: ideally Gouldians. I'd especially love to watch them raise some babies. However, if I were to add a female to my male pair in the F030, would that cause pure havoc and chaos? The males get along great, no plucking, no fighting. They cram together into a little nest-thing every night. One of the males constantly sings and tries to court the other male, who just looks at him like, "C'mon, man, this again? I told you, I'm saving myself for Sarah." I'm sure if I had problems I could separate out the bullying/bullied bird back into the cage I already have, but I want to know if this is something I should even try to begin with! (Also, I was hoping to use the cage I already have for babies in the future, provided this works out.)
Long story short: do y'all think I would be able to house more than a breeding pair in the F030? The cage calculator on this site says the F030 is fine for 3-4 birds. Would an extra bird cramp the style of the breeding pair? Or should I scrap the idea of the breeding pair altogether and maybe consider adding another same-sex Gouldian to my male pair? Or... alternate suggestions?

Thanks so much,
Ash