If you want to find out about sex links read the very first post in this thread. It takes a bit of thought and study but once you grasp the concept, it is not that hard to follow. There is a chart there that tells you which rooster will make red sex links over your Delaware hens.
Tadkerson’s Sex Link Thread
https://www.backyardchickens.com/forum/viewtopic.php?id=261208
Some people think there is something magical about sex links. There’s not but some hatcheries sell commercial egg laying chickens as their sex links and a myth is born about sex link egg laying ability.
If you put a buff rooster or any other red rooster over your Delaware hen, the chicks that hatch will be yellow it they are male and red if they are female. That way you could sell day old chicks and guarantee that they are female. Your customers might like that.
One problem for you is that the same rooster over your red hens will also give you red colored down on their chicks. If you hatch eggs from both, you won’t know which red chicks are pullets from the Delaware and which could be either sex from your reds. I’ve done that. You really can’t tell. But the yellow ones will definitely be male.
Every chicken breed was created by inbreeding. Every grand champion chicken at a major chicken show is created by inbreeding. Practically every pioneer family that settled this country kept flocks with a lot of inbreeding. Inbreeding chickens is not as horrible as some people believe.
When you inbreed you find out what genetics may be hiding in your chickens. These may be good genes or they may be bad. Often you have some of both. By carefully selecting your breeding birds to be the ones you want and by ruthlessly making sure the birds with bad traits don’t breed, you can improve your flock. You may also find out that your flock has some really bad genes and you really need to start over with new birds.
Inbreeding can cause problems if you don’t know what you are doing. Championship breeders carefully select their breeders and can keep going with inbreeding for decades or longer. Most of us are not that good or don’t have the facilities to use the techniques they use. One standard method, spiral breeding, involves keeping three different flocks and keeping really good records of which birds breed with which, for example. A real standard way to handle this for many of us is to bring in new blood every five years or so to keep the genetic diversity up. You still watch which breeding birds you keep and you don’t know what genes you may bring into your flock with a new rooster, but this technique has kept a lot of flocks healthy and producing for thousands of years without spending a lot of time and effort on tracking genetics.
As far as timing, whenever you can do it. People will argue that this is better or that is better and they may have a good point, but to me the best time to do something is when you can.