No, they do not take less maintenance than a composite breed. A foundation breed takes just as much hatching, judgement, selection, and culling as any other breed to develop your flock to SOP standards. Also, the more rare the breed, the more important it is to select properly, as just a few prominent breeders can change the direction the breed takes, for better or worse.
Yes, you can breed hatchmates to each other, as long as you use a rolling breeding program and careful recordkeeping to avoid too much inbreeding. (You can ask your hatching egg supplier if s/he has multiple breeding pens set up. If so, you can ask that the eggs be marked as to which breeding pen they came from. That would allow you to avoid full brother/sister matings if you want to.) Most flocks are started that way. There are many well maintained breeding flocks (in general, not specifically of Dorkings) that are over 100 years old that started with a single shipment of birds, and have never brought in outside genetics. Mammals are more affected by inbreeding than birds, but that doesn't mean that birds are unaffected. Care and selection is required for success.
Rose Comb Colored Dorkings, while beautiful, are a very ambitious challenge for a breeder. The Colored Dorkings are difficult to breed true, quite uncommon compared to the other colors, and often require two separate flocks to maintain the proper SOP color -- one to breed the right colored males, and one to breed the right colored females. Since the rose comb is not the SOP for this color, your stock is limited to either the few breeders that have already started this project, or to obtaining Single Combed Colored Dorkings and perfecting them, then later adding in the rose comb. Either way you won't technically be "conserving a breed," since the RCCD is not technically an SOP breed, but that doesn't mean that it isn't a worthwhile project, or that you can't contribute to the improvement of the qualities of Dorkings in general. You should probably PM someone who posts as Rockashelle on BYC. She has been working with RCCDs for several years now, and can give you some insight on the rewards and frustrations that she has encountered.