Looking for premises near Covent Garden for a dance school with accommodation

I’m helping out a friend who is new to the property world and wants at the moment to stay anonymous. She’s looking for a leasehold of an entire building as a long term investment. The purpose is to run dance teaching classes with social dancing events and dinner shows also. 

Location: Ideally Covent Garden/Holborn/West End to capture tourist market for dinner show and for transport links, recognising potential planning restrictions if change of use is involved (previous use as a restaurant could work). Area south of Holborn/east of Kingsway (LB Camden) could have possibilities.

Main requirements are:

• main room to be minimum 250 square metres (can be basement level, no direct street view required, can also be back of building)
• additional room of 40 square metres
• small office
• kitchen
• toilets to serve the possible maximum occupancy for events

Residential accommodation on upper floors (self-contained flat(s)) would also be of interest.

Questions:

1. What would be a usual length of lease for this kind of property?
2. What would be a desirable number of years still remaining on the lease at the point of resale in the future for the property to remain marketable at a good price?
3. What would be a likely purchase price currently for such a property?
4. What is the best strategy for finding suitable properties?

Any other comments or pointers welcome!

Many thanks

Sue Whittle