private node groups

I have a problem I am trying to sort out.

I am trying to create a small inventory system. What I was thinking was creating a content type Inventory with the required fields and then a user can add them and so forth. However I am trying to figure out how to accomplish a few things.

One issue is how do I create it so that only specific users can view that node. Lets say I have two customers with two types different sets of inventory I do not want them being able to see each other inventory lists. This would be able to be linked to their customer ID but I am trying to figure out how I would be able to do that?

Issue two I want to be able to "check out" items. This would mean when I want to deduct the quantity of an item I want it to ask me for a autho number. Not only do I want it to be able to ask for the number I would like each item to keep a history of the deductions and additions to quantities along with the autho numbers and the user who changed it.

Please let me know what I need to do or how I need to accomplish this. I am playing around with a few ideas but I really am at a loss.

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Andrew