Assuming your mortgage company allow it:
Landlord insurance for non-payment of rent, damage etc - but also, what won't the insurance cover? If your tenants disappear with a year's unpaid rent, having ripped out your kitchen, broken the bath, pissed on every carpet, punched a hole in every door, wall and ceiling, how will you pay for the repairs? Can you afford to deal with this?
Do you want to manage it yourself or use a letting agent to field day to day issues and emergencies? What % will they take from the rent for this? What do their tenancy agreements look like - break clauses etc - are they onerous for you or your tenant?
How often will you want inspections carried out to ensure it's not going to be trashed / turned into a cannabis farm / housing 14 people it's been sublet to? Who will do them?
Have you got all the certification? Gas, Electric certs, EPC rating etc. Plan for the annual checks and ensure you know how much notice you have to give your tenants to carry them out.
See if your council area have a Responsible Landlord-type scheme: www.cornwall.gov.uk/housing/private-housing/cornwall-responsible-landlord-scheme/
Deposit schemes - ensure you have one you'll use to protect your tenant's deposit.
Meter readings - ensure you do them before you move anyone in and again when they leave. It's the tenant's issue, but you can save a lot of hassle this way!
A full and complete inventory is the best way to protect you and the tenant from disputes later down the line.
Be realistic about what wear and tear looks like - worn carpets, marks on paintwork, chips in paintwork, scuff marks on kitchen worktops might be considered reasonable, especially if a tenant has been in there for years rather than a week. You will have to budget for replacement of carpets, repainting of the house etc and your tenant cannot be expected to pay for it all - it's natural wear and tear and to be entirely expected to happen in the course of living. Damage is different.