Hi, I rear pure dairy holstein friesian calves, there is a small amount of profit in this, I just tend to do it as a savings plan more than anything plus the pure enjoyment of rearing them. I also buy beef x dairy heifers to bring on to put back in calf to a beef breed, have been successful in this and left calves with their mother and fed them with them up to 8 months and was offered £850 per calf from a local farmer just prior to the winter, knew he would make a profit come the spring but outweighed the cost of feeding etc over the winter.
You need to bear in mind whilst there is viable profit in some things I paid quite a lot for a belgian blue x friesian bull calf, lovely big strong healthy calf, took pneumonia and despite being treated with numerous things to the tune of a few £100 I lost him. These are things you have to take into consideration, rearing of calves isn't a doddle but it's a great thing to do but building up knowledge, being able to recognise signs of illness and any problems etc puts you in a far better standing for starting this from scratch, plus it is labour intensive if done correctly. I reared calves for a number of years learning by trial and error, then I worked full time dairy rearing calves and milking etc, that taught me an awful lot and was a great experience, I still work in the dairy industry as well as running my own place, hence the access to a number of farms in the area.
If you want an easy option and profit calf rearing isn't it, although one of your other ideas maybe be a hit depending on where you are located, the horse side, field livery etc. Breeding horses now is a no no really value is right out of them.