I am glad you are not planning to rush into breeding, giving you a lot of time to get lots and lots of knowledge beforehand on how important it is to breed budgies.
Have you considered what you will be doing with the baby budgies?
Here are a few links to look over for now.
A heartfelt plea to forum members new and old
Are you ready to breed budgies
A Budgie breeding diet
As for pairing budgies, it can be very challenging. I do not breed budgies, but I have 8 budgies, 4 males and 4 females. They have managed to settle into comfortable pairs. I had two males together before I got any females and they got on incredibly well, snuggled together at night and were very close. Once the girls came along, it changed straight away.
Jay, is incredibly hormonal and can now only come out with his cage mate, Sage. The pair have never mated and when he has out of cage time, I cover up my other cages as he will otherwise constantly bother the females and aggravate the males. The pair get on very well themselves, and even though they have nothing that should make them want to settle down and nest, they have not got that instinct with them anyway.
It also concerns me that you mentioned 'continually buying females'. What would you be doing with these females that did not bond with the mate.
I think you need to seriously consider the full implications of breeding budgies and what this might do to your current budgies. I feel like the boys seem to get along quite well and adding females might not help.
Plus, ideally, you would be housing these birds in a new cage for quarantine and when if they do bond, you would want to split the pairs into their own cages.
I'm sure some other members will have some advice for you too.