I assume the sacrifice of 20% of your income for limited periods involves its use by a family member, like a student home for the vacs or some suchlike. If their visits impinge on your peak occupation periods you are looking at possible income shortfall problems. Do you have space for a suitable caravan your occasional visitor could use?
If it is a good established B&B you will have regular repeat business so will be able to predict some cash flow, if however it relies to a large extent on passing trade, you will find as I did when I did B&B for a bit, some nights you pray for a knock on the door, while others your sleep can be disturbed at midnight by people looking for a bed.
If it is not already on the internet get it on there, offer discounts for early bookings with appropriate non refundable deposits, and look for a unique selling point, you're into folk music use that to sell it to like minded people.
Giok