If Aang and his children retain this quality, it will take more than a century to even have a community of Airbenders.
True but you gotta remember pleh, the avatars usually live long lives. They usually don't die until they are in there 80's or higher. And you figure even if it took a century or more to create a whole community of airbenders, that would be enough time until the next air nomad is called to be the avatar. Like the next water nation avatar after aang dies could live to be 85 or 90. then the same for the earth and fire nation avatars. So saying 80 is the average number of years of the next three avatars life span, thats around 240 years right there. So even if they never did soulbending that's plenty of years to repopulate.
and yue was 16 when she was of marrying age, so you gotta figure that they can get married at a young age. With that in aang and katara's mind they just might get married at a young age and maybe 5 years or so after they get married, they would think about having kids cause im sure repopulation will cross their minds. So it sounds like both theories would be a good idea, but even without soulbending it sounds like they have more than enough time to repopulate.