If he is a white park x wagyu, how do you say he is a mini???? Did I miss something in a post? Both those breeds are "full size" cattle.
How old are your heifers? Do you have a source for a few feeders until you start to get a regular routine, and supply of calves? 8-9 acres is not going to be enough if you are trying to mostly pasture raise. Especially if you are wanting to try to finish the beef on grass as much as possible. You will have 4 "sets" of cattle, not 3. Cow with calves, weaned calves that were last years calves, long yearlings that will be the calves from the previous year, and the 2+ yr olds that will be getting finished.
Cattle do not marble good, until they get some age and maturity. Wagyu also take longer to finish to marble properly. And requires a bit more intense feeding. You will be killing in the 25-30 month age, or older. If you want any thing like t-bone etc. they have to be killed before 30 months in order to follow the federal regulations for possible BSE which is what causes the Mad cow and possible Creutzfeldt - Jacob disease. Sure, your animals could be totally "clean" but if they are butchered in any inspected facility, you cannot get any cuts with bones that are part of the spine if you kill after 30 months. I do NY strips and filet instead of T-bones to not have to worry about the BSE rule of age; but I do like to get backbones for cooking like ribs so try to usually kill before 30 months.
I have beef in the freezer that is VACUUM PACKED that is several years old. Done right, it will keep for years in the freezer. If I find myself with some extra left over beef and another that is getting ready to be killed, I take it to an old order Mennonite, that makes bologna, beef snack sticks, fantastic hot dogs, chipped beef out of roasts etc. It is not cheap, but I like knowing where my food comes from. There are places that do just that.
Are you equipped to handle a young bull that has nothing to do for months at a time? A 1200 lb bull is nothing to sneeze at. Most of our bulls will hit the 8-900 lbs by a year and most of our mature bulls weigh in the 17-1900 lbs. Mostly angus. So a 1200-1400 lb bull is closer to normal size than mini. 1400 is not ALOT smaller than a full size bull at nearly a ton. You will not be able to stop a 1400 bull any easier than a 18-2000 lb bull. If you let him run with the cows full time, you will have calves at random times. Cows can get bred back sooner than they should and calve at less than 12 month (yearly) interval. That is hard on a young cow, but not as big deal for a mature 5-6 year old animal. They are as mature as they will be by then, but as a 2-3 yr old., they are growing and really do need to be not get bred back too soon, so that they can carry a pregnancy, and feed a nursing calf, AND STILL GROW themselves. You will need a very secure pen/pasture, to contain the bull because when he gets a sniff of a female in heat across the fence, he can very easily go to her. Even really hot electric sometimes does not stop them.
You will be feeding an animal for many months when he is not earning his keep. That can make some of them very grumpy.... it is simply frustration.
Whatever you do, do not make the bull a pet. Respect him, keep him friendly, but do not treat him like a puppy dog. YOU have to be the head of the "herd" ..... they have to respect you. Do not deal with the bull from face/head on. Halter breaking and all is fine. But do it from the side. A bull establishes his position/dominance from a point of pushing. They will hurt you if they start to get pushy. Same as with a ram or buck goat.
Also, be careful about breeding "mini breeds" too young. Make sure they have enough growth. There are alot of breeding problems with mini's and fertility is one. Regardless, of what all the web sites profess, there are definitely some breeding concerns. I have done AI for over 40 years. I have seen it in all breeds and sizes, but the mini's have some unique problems. Let their bodies get some maturity or you will be pulling calves and losing animals. We have to pull calves sometimes in the full size cattle, especially if you do not pay attention to the crosses you are making. Highlands are a naturally a smaller breed. You need to be very aware of what you are using to breed these crossed females. Do you know much about the bulls breeding besides that he is a cross? We use bulls that have genetics for "easy calving" for our first calf heifers. This is still not a guarantee that the calves will be small but it is a better chance that the resulting calves will be smaller and easier for a first time heifer to have it. You try to get the odds in your favor. You also have to be careful of the dwarfism gene and breeding animals that have recessives.
The pictures look like some nice animals. They are cute.