At no point in time would I recommend to anyone to use mongrels of unknown breeding as the main dogs in ones pack. Their pups are worthless and they don't breed true. A pair of mongrels that are firecrackers in the bush have very little chance of producing pups that perform to the same level of excellence as their parents and as I said THEIR PUPS ARE WORTHLESS. Why keep dogs that produce chancy pups and whose excess pups you have to give away. Dogs cost money to maintain properly, if you're gonna keep dogs keep good dogs. The only reason I see to keep a mongrel is if you plan to use it as the foundation sire or damn of a new breed of dog.
If you do plan to start a project of planned crossbreeding, first you must know what you want or have and only use unrelated breeds that are similar in working style. I know this is very over simplified but this is what I would suggest you do. Base the program on a female, that way you can take her to any number of stud bulls, if you base it on a bull you will have to buy several unrelated bitches. A basic breeding plan is as follows, keep only bitches and use bull pups sold as future studs. You will have to keep track of all bull pups sold, so that you can judge them as adults an choose the best for backcrossing.
FIRST BREEDING(OUTCROSS):-
Foundation bitch (A)-x-(B)outcross bull#1=>outcross litter#1=(OCL1)
SECOND BREEDING(OUTCROSS):-
Foundation bitch (A)-x-(C)outcross bull#2=>outcross litter#2=(OCL2)
FIRST LINECROSS:-
(OCL1)bull-x-(OCL2)bitch=>linecross litter#1(LCL#1) ---> half brother & sister cross
SECOND LINECROSS:-
(OCL2)bull-x-(OCL1)bitch=>linecross litter#2(LCL#2) ---> half brother & sister cross
THIRD LINECROSS:-
(LCL#1)bull-x-(LCL#2)bitch=>linecross litter#3(LCL#3) --->cousin & cousin cross
FIRST BACKCROSS:-
(LCL#3)bull-x-foundation bitch(A)=>backcross litter#1(BCL#1)
A good bull from this cross can be used a proponent stud bull on any bitch in this breeding program.
While all of this may look good on paper remember that the true test is in the living flesh, see what the dog looks like and how it hunts before using it in you breeding program. When you linebreed, backbreed and inbreed you are doubling up on the genes of the dogs that you are backbreeding to in varying degrees of severity, so expect very good and very bad pups in a litter. It all depends on what lurks in the genes of the parent stock. Both the cream and scum rises to the top when you backbreed. Ounce you can cull/kill defective pups and not let them survive to further taint the gene pool of your strain and give yourself a bad name as a breeder, the quality of you strain will improve over time. That's the goal of us all, to improve our dogs over time. Just take your time, know what you want, don't lie to yourself when judging dogs and don't be kennel blind. Good luck with breeding your super dog.