I am not quite sure what it is you are seeking, so I'll try and cover a couple of points.
Many tenants receive Rent Supplement from (now) the Department of Social Protection (but this may be handed over to the local authorities already or soon for administration). This can be paid to thye tenant or to the landlord.
All landlords are required to register with the Private Rented Tenancies Board and pay the Non Principal residence Tax.
Landlords may set off, against rental income, up to 75% of the interest on their buy to let mortgages as well as other expenses.
Hope this clarifies the issues. Many threads here on taxation and set off of expenses in Property Investment forum.