Think this one is a good move:
3) I will be updating each product with better supply information stating if it's in stock, how many we have and if not how long it will take. With the reduction in items as above this will be far more manageable.
I can understand that for exothic parts you don't have stock and that these items are "on order". Lots of people think it will only take you one email to japan and they'll have the parts on there doorstep in a few days. I also got a small business in Holland and I can tell you, this is absolutely not the case. (Try to get something fast from Whiteline for example
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You're better off informing the customer that it isn't in stock and it could take a long time. Maybe only charge a down payment for this type of orders. This way you'll avoid these kind of situations.
About replying, try using the MS Outlook "Out of office" function to inform your customers. This will give them a custom reply on you current situation. This way you can inform them that you're not able to reply and when they can expect a reply.