Jackie, I recommend AI as well if you only got 10 cows to look after. A bull has a tendancy to ruin fences and induce complaints from your neighbors if he don't have other females to service after the 10 have been done. Because the only way you'll keep a bull happy is if he's got a bunch of ladies to service and food to eat.
Heifers and cows come into heat at different times. They won't necessarily by cycling en snyc, so will be needed to be adjusted by a short of PGF2alpha (something like that) in order to come into heat at the same time to make for more efficient servicing via AI. Naturally servicing heifers or cows need to have a breeding time frame of 45 to 60 days for the bulls to cover all of them. Those that don't get covered should/will be sold at the auction.
DO NOT, on all conditions, wean calves with the horses! You will really be asking for a train wreck and some very hungry, stressed out calves that have been terrorized by the more aggressive horses. Cattle and horses do not mix, thus should be kept separate, except if the cattle outnumber the horses by 5:1 or greater on occasion.
So with that, you'll need to really think out a fencing plan to keep the horses and cattle separate. A drylot for the horses is good for when they are not needed out on pasture, and cattle can have access to pasture 24/7. I do agree with the rotational grazing idea, especially if you are only using the land for trail rides and grazing.