For the first point, not sure what you mean by the 'name tab' or the 'tab name'. Could you clarify?

For the report text, go into the company configuration, then the header/footer tab. Inside the header tags is some code that looks like this:

    <!-- left margin -->
    <rotate degrees="90"/>
    <fill color="grey"/>
    <drawString x="2.65cm" y="-0.4cm">generated by OpenERP.com</drawString>
    <fill color="black"/>
    <rotate degrees="-90"/>

Delete this block from the header, or replace with your own text if you wish.

Where do you want to put a picture in the purchase order? On the report itself? Attached as a document? On each purchase order line?

When you receive a shipment, you have the choice to alter the quantity received. If you receive under the total amount, it will create a backorder record for the remaining items. So, if you order 100 shirts and get 85 in, change the quantity on the confirmation popup to 85 and your backorder will be created for the remaining 15.