My parents owned a house 30 years ago that they rented out so on the back of that...
We went in April to open it up and October to close it down - both 'holidays' were spent cleaning and doing maintenance.
Summer was a holiday there. No point going anywhere else as staying in our house was cheaper.
You might want to go in peak weeks so you'll make less money.
We rented to friends, but renting to other people seems to mean they can break whatever they like and not take care of anything because they are paying for it. So factor the cost of repairing things.
Our friends understood that they had to clean the property for the next people, you might need to get in a cleaner - more expenditure.
Our next door neighbour used to mow the lawn but you might need a gardener - more expenditure.
Have a look through mumsnet at all the private landlords and the state their houses can be left in. Also, the moans and groans from tenants about how shit their landlords and estate agents are. Maybe dip into the holiday cottage ones too. That will help with the possible pitfalls and will enable you to see what sort of agent you need to look for!