Hi Ghengis.
I used to run a few backpackers' houses in London up till about 4 years ago. Classifying them as B&Bs made it possible to get around the problem of having tenants' agreements.
Here are some pitfalls you might want to check:
contact the council local to the house you have in mind. Ask them to send you information about their council business rate charges. You will, I'm afraid, have to pay enormous sums for this.
Also you need to find out about health and safety regulations, fire regulations etc. You will need a fire alarm system and fire doors, fire-protected staircases and safe furniture. Make sure your windows are openable so that people can escape through them if there is a fire.
You might need planning permission for the use of the building.
You need to ensure there is adequate parking.
Don't get the place if it is not easy to reach by public transport. The nearer a station the better.
You will need to use a laundry service or equip your house with a big laundry room with at least two washing machines and tumble driers. (Obviously depending on the number of rooms).
Be prepared to have inconsiderate guests sneaking in unpaid-for friends, playing loud music and TVs late at night, knocking on your door at all hours to borrow every little thing, etc etc. You will have to go out if you want some peace.
IME the higher the standard of decor and service you can offer, the more you can charge - and crucially, the more considerate type of guest you attract.
Charge a deposit to stop people doing a runner on you.
You will have to get a special buildings and contents insurance package.
Be prepared for anything - in 10 years in the business I have dealt with plagues of vermin, thieves, immigration police raids, guests being arrested, guests reporting me to the authorities, being taken to court by the council over their mistake, guests growing cannabis in the garden, guests using drugs openly in the house, guests damaging things etc.
The good thing is I did make a lot of money out of it and still have friends all over the world with whom I exchange emails all the time.
Email me or post again if I can help with any other concerns you have.