1) Interact with QuickBooks. There is a module available that will export a day's transaction details into a QuickBooks file you can import.
In the same theme, it also integrates with SQL-Ledger in real-time, as opposed to batching up transaction details like the Quickbooks module does.
2) I'm not sure about printing UPS labels. I wrote code once for Interchange that produces FedEx labels by using FedEx's Ship Manager API (and even then, FedEx makes the label images themselves, and the code just downloads the file for you). UPS makes a similar internet API, but I haven't tried integrating Interchange with it yet.
Printing UPS labels from the database would be possible given a UPS account and some developer time to write the code.
3) Metadata can be added to any page, including product pages. Interchange can either generate a page for a SKU from a template, or you can build a custom page with the HTML laid out exactly as you want for a specific SKU (and you can mix both methods, too).
Adding metadata to the template-built pages would work something like the following. Editing "flypage.html" in an Interchange catalog's directory:
<meta name="keywords" content="[item-data keywords]">
<meta name="description" content="[item-data description]">
The tags in brackets are IML (Interchange Markup Language). In order to do the keywords you'll need to add a "keywords" column to your product database, because it doesn't have one by default.