Hello, I am Keith, one of the experts on Jujst Answer, and pleased to be able to help you with your question.
1. Only the letting for the period. Advance bookings should be credited to a suspense account and then debited when the net rental is received.
2. Exterior painting is not a capital, but a revenue item, and is allowable against rentals in the Corporation Tax (CT) computation.
3. Yes, providing that the costs were wholly and necessarily incurred in the operations of the business [UK tax rules].
4. The UK and Spain have a Double Taxation Convention which precludes the same income stream being taxed in both jurisdictions. This is achieved by means of tax credits, the tax paid to one country being allowed as a tax credit against the liability in another on the same income stream. The Comvention does not protect you from differences in rates of taxation. You have to make a supplementary return on a Form SA106; this form makes provision for claiming Spanish tax credits.
5. Spanish VAT is an entirely different system and should not come into the UK taxation computations.
I do hope that you have found my reply of assistance.