Cattle management is primarily about keeping them fit and well, balancing the cows condition using electric fencing (stopping them getting too fat if grass is lush), and making the grass last as long as possible by making them eat it down hard. Devons are perfectly suited to this regime. Calves are creep fed until the end of their first winter.
Usually just the calves come in for the winter, going out in March-April to allow the cows to come in to Calve.
Worming and fluking is annual for the cows, usually in the autumn-winter, but youngstock get wormed more often. No other medication is routinely necessary.
All male calves are castrated in their first autumn, after growing well with the testosterone over the summer. I don't have facilities to keep a bull, so if a good one comes along it would need to be sold as a Yearling.