First, create two Customer Groups which you'll use for separating products/prices for different groups.
In order to restrict some products for first Customer Group, you can use extension
GroupsCatalog extension. It allows you to do any kind of restriction by customer group.
For second part four configuration, you can set up quantity discount via:
- tier prices (check this link)
- set up catalog rule based on customer group (magento admin -> promotions -> catalog rules)
- set up shopping cart rule based on customer group (magento admin -> promotions -> shopping cart rules)
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