I look at this a bit differently than some of the previous posters. What distinguishes you from many of the dreamers that show up with similar requests for information is that it sounds like you and your husband have enough experience to actually restore a big boat and run it in the charter trade. But that does not change the reality of this particular situation.
I will say that if you are truly going to do the charter thing, then it is critical for one of you, if not both to become licenced captains, and to completely understand all aspects of the charter business (Boat building standards for charter boats, Boat Maintenace, International Charter regulation and law, Marketing, Insurance, CPR/First aide, Scuba supervision and rescue, Preparing a viable business plan and obtaining long-term and short-term operational financing, catering and special diet planning, local safe and dangerous flora and fauna, let alone how to safely operate a big boat with know-nothing charterers on board and so on). Unless I missed it, neither of you current have a captain's ticket. That is the minimum price of admission.
I think that a 50 footer is pretty much the minimum practical size for a crewed charter with 55-65 feet being a more ideal minimum range for a crewed charter boat that you personally intend to live on. (Owner-operators are a very different situation than a captained charter boat owned by an absentee owner using a paid crew. Paid crews will live a lot more spartanly than owners who need the boat to be a base of operations for their entire life and the management of their chartering business.)
To be frank, even in boom times, boats like the one in question have a negative value, meaning that the materials and equipment alone to restore a boat like that would cost many times the value of the boat in perfect shape. In this case, the design is so mediocre that it will never be worth all that much as compared to better designed boats with better pedigrees.
Further reducing the value of this particular boat, or any boat needed a full restoration is the matter of restoration time. Even if you and your husband are tallented boatwrights and can put in 10 hours a day, seven days a week, and have a great boat shop with all the tools, turning a hulk into a boat that is safe, reliable, fully equipped and attractive to charterers, would take many years (my guess is three years minimum) during which you could be off sailing and earning money to support your dream.
Having helped prepare the calculations and documents for a boat that would simply be in the day charter business and watched the USCG certification process at work, getting a boat certified as suitable for charter is not for the faint of heart. There was a whole lot of paperwork that needed to be filed and a whole bunch of inspections that had to take place during construction. It can be done but It would not be the easiest process for someone to go through, especially someone who is early enough in this process to be asking," What are the regulations governing Charter boats?" (I don't mean that to sound critical or disrespectful in any way as I understand that we all go through a learning curve whenever we start a new venture.)
But that all brings me to my central point....In these times there are lots of super boats out there at bargain basement prices that are ready to go. I would suggest that you look for a fully operational boat that needs some aesthrtic help and perhaps instruments and mechanical upgrades. People like charter boats that are 'pretty' and offer reasonable preformance. The boat needs to be able to carry all the toys. I would suggest that you look for boats that were well built to begin with and which are structurally sound. Ideally, I would suggest that you look for a boat that is already in the charter trade since its certificates could be updated rather than created from scratch.
Here are a couple models that might give you an idea of what I am suggesting.
Bowman 57 1975 Bowman Ketch Sail Boat For Sale - www.yachtworld.com
Lavranos 56 http://www.yachtworld.com/core/listing/boatFullDetails.jsp?boat_id=1961780&ybw=&units=Fee t&access=Public&listing_id=1791&url=
Tayana 55/56 1988 Tayana Cruiser - Center Cockpit Sail Boat For Sale - www.yachtworld.com
Farr 58: 1987 Farr 58 Center Cockpit Sail Boat For Sale - www.yachtworld.com
Camper Nicholson 55: 1971 Camper & Nicholsons Center Cockpit Yawl Sail Boat For Sale -
Deerfoot 61: 1988 Deerfoot Sail Boat For Sale - www.yachtworld.com
Swan 57: 1978 Nautor Swan 57 Sail Boat For Sale - www.yachtworld.com