Hi Ralph - Room size appropriate for a hands-on class is always a difficult question to answer.  As you point out there are many variables that contribute to getting it as right as possible.  I'd start with building and room capacity (sometimes easy to get and other times not so much) and then look at the size and scope of the layout of the room and materials and tools in use.  We have rooms at RISD that use different layouts for different types of classes - desks have one capacity but that changes if there are workbenches, etc...For example, if students are using just scroll saws the clearance for work is different than those using a table saw - might review equipment manufacturers owners manuals for that info.  Then consider electrical needs for equipment - can you have 15 students competing for 5 electrical outlets, maybe maybe not.  At that point extension cords and other trip hazards can limit class size - so one size doesn't fit all for sure.  Maybe easier to find out the maximum class size and work backwards for there.  Hope this helps - Alan c