Hi Macoto,
Firstly, for everything related to my BTL properties and finances, I have a separate bank account. Therefore I can keep clear track of everything that goes in and out of the account.
In the first instance of buying a BTL, depending on the work required or developments you may look to do, just keep a folder / filing cabinet for every bit of documentation you receive, whether these are quotes, invoices, recipts, gas / electricity certificates, etc, as soon as you get it, file it away. Therefore when it comes to tax purposes or an accountant (if you were to get one),you will be able to supply everything that is required.
For each BTL property, I keep £50 a month to cover any unforeseen issues, or to go towards decoration, etc each year. Generally, even if your tenants were to up and leave once a year, you would hopefully only have minimal decoration and cleaning to do each time, sometimes you won;t need anything done except for cleaning, but over the course of the year, that £600 will make life so much easier as and when a more expensive issue was to arise, drain issues, chimney blockage, boiler fail, etc.
Also, if you were to have a property using gas, I'd suggest looking into companies who supply some form of gas / boiler maintenance. They vary in price due to the type of cover these consist of but some will include an annual service and Gas safety certificate which is a mandatory requirement for any property using gas. As an example, I pay £16 a month for one property which is £192 over the course of the year but this covers the annual service (usually £50+) and a gas certificate (usually £70+) so in effect I'm paying £70 for peace of mind of a service that also has free call outs, free radiator checks as part of the annual check, a low excess (£25) and some other advantages which when compared to afew other quotes was a great deal for me.
Hope that helps and good luck to you
