Here are a few thought on your situation which you might find of use:
There will always be a demand for play space such as yours, from those who either can't have their own space where they live for various reasons or from those wanting to meet up with a play mate in a more convenient location (i.e. London is midway between their respective locations or is simply easier to get to, particularly if one player is based abroad. Hotel rooms are always available as an alternative but aside from the Black Tulip (Amsterdam), the availability of privacy combined with on site equipment is limited.
No idea how much you should charge but you might want to consider renting the space out with only the larger (none moveable) items e.g. sling; piss pool included in price. Smaller items such as gags; hoods (which are prone to disappearing due to size) are often the things which people already have and can travel with anyway, therefore there is no need to provided them along with the room unless requested. Such items could be made available on an individually priced basis. Those items requested can be provided along with a receipt which can be signed, both when being handed out and returned, thus protecting both parties from later allegations of damage or loss.
Depending on how 'official' you wish to make it; the 'contract' to use your play space could include;
a) non use of illegal substances and certain types of play (e.g brown). Not only to protect yourself officially but even if you have no intension of enforcing any ban, you will probably want to ensure that it isn't you who ends up clearing up used pins; spillages of lube or body fluids etc;
Permitted noise levels at various hours of the day and night;
c) Expectations on how clean & tidy the space is left after use;
c) Number of persons allowed to use the space at any one time.
Hope it goes well.
