Property: Size & Commercial Contracts

Hi Everyone!
- just a couple of questions I've got on my mind at the moment. I'd appreciate any input or experiences. Thanks in advance. :)

A Small 20 Bed Hostel
We're looking at starting a small (20 Bed) Hostel in North-East Europe but we're unsure of a few things concerning how big the property should be and the rental contract challenges we could face:

(a) How many m2 is appropriate?
How many meters square would be appropriate (in your opinion) for a 20 bed hostel. m2 should include absolute all space used, kitchen, front desk and dorms.

(b) What experiences did you have with obtaining a rental contract?
We're looking at various rental properties. A lot of ideal properties we've found are listed as commercial rental properties... We're wondering if the realestate will struggle with the idea that we'd like to use the commercial property as a hostel. How did you find your property? What flexibility did your lease afford? Is it possible to build walls here and there on a commercial contract? What should we expect?