Here's the thing: folks who are serious about preserving these breeds typically keep about 10% of what they hatch. You need to hatch hundreds in order to move your flock forward. To be in a situation to be able to do so requires more space than areas where you can only have a handful of birds. Helping others by hatching for them - that's fantastic, and I'm sure you've done and will continue to do a ton of learning in the process. So - do what you can!This is so funny to me!
You do not have to sell your house and move to the country to help preserve Heritage Breeds.
As an example, I live in the city and am only supposed to have 6 hens. I have already hatched SG Dorkings for a local breeder. Next Year, I will be partnering with the Breeder to hatch a lot of chicks for her. I will also be keeping Roosters at her place in the Country to breed with my own projects. I am working on Penedesencas and EO Basque. I may work with Heritage RIRs too. I will at least hatch a couple of dozen Heritage SC RIRs to share with local breeders in my area.
Keep on learning and encouraging!