1 Do I have to have done any Agri courses to get a herd number?
No
2 Is it necessary own land or will a year on year lease do?
A written lease will do; not sure if a one year lease is acceptable. Ask at your local Teagasc office.
3 Will the retired farmer still retain his single farm payment etc???
The rules are complex and of course they are subject to change. I think there is a clawback if entitlements are leased. I think that some entitlements cannot be transferred or leased; In any given year, you have to use them to be paid out on them, so if the farmer leases the land to you, the entitlements are no good to him for the duration of the lease. Of course, he might have a situation such as 40 hectares of land but only 20 entitlements (unusual but possible) in which case he might be able to lease 20 hectares to you and keep 20 to cover his entitlements. I hope this gives you some flavour of the needless complexity involved. Really, the farmer would want to get full and detailed advice specific to his situation. Teagasc are generally good on this stuff, as are most of the private agricultural advisers and some rural solicitors.