Mark wants to design a new case just for harp players. Here are some thoughts to his questions.
1. How many 10 hole diatonics should it hold?
Well, I'm influenced by a few factors here. If I'm going to a jam situation, I want to be prepared for anything. If I'm heading to a gig of my own, I only need to bring the harps I know I'm going to play. I kinda prefer NOT to carry excess harps because I don't want to make it too tempting and too easy for a jerk to steal all my harps at once. Major key harps come in 12 keys, minor harps come in 12 keys, and "country tuned" harps come in 12 keys. There are also some special low and special high tuned harps, so if you wanted, you could make a case with more than 40 slots. But that would be a real big case, and over- kill for most harpist. Better to make the case smaller, and let the player buy more than one if he or she wishes. IMHO the finished case should be no larger than the average attache case. Smaller is better. I think Hohner may have the answer with their case that hold's 12 diatonic harps and a chromatic. That's one possibility. If you go this route however, the only difference between your case and Hohner's will be the styling and the price. You might consider a case with a dozen "extra long" slots. If each slot is in fact big enouph for two harps, the player will have the option of packing more than the standard 12. He or she can carry back-up harps for the more vital keys, or a couple of minor or country tuned harps etc. Perhaps you should make a standard case (12 diatonics plus a chro) and a "Super" case with the extra long slots.
2. How many chromatics/big harps should it hold?
If you're looking to make a harp case for the masses, I'd suggest a case that holds only one or two chros.
3. How many bullet mikes should it hold? 4. Should it accomodate other types of mikes? 5. Should it hold mike cables?
IMHO this stuff can travel seperately.
6. Should it accomodate other things?
Yes. It should accomodate the player's business cards.
7. Should the overall appearance of the case be high tech or retro, ie. tweed, etc.?
RETRO! RETRO! RETRO!
8. What should the cost be?
Hohner makes their case for $40. I think you better keep it under $75.
9. How important is durability?
It should last a life time. It should protect the harps when dropped from high places, and when sat on by large people.