Not sure how to breed....

So I have recently come back from a large break and want to get back into the game. I was thinking about actually starting a line but not sure how to start or where to begin. I want to breed to help current players in the game with their lines not something that is not gonna sell but I also want to use horses that are in the RC to reduce the amount of horses just sitting around in the rescue center. Any advice on how to start a line like how many horses, how to pair them, etc. would be very helpful. Also what are you all currently interested in. I want your preferences especially if you are very active to help gauge what I should breed once I figure out how to breed that is XD. Thank you all so much for your advice and info :)