'Would it be possible to connect the printer by usb to the TP Link wap to do this using a TP Link ethernet port?' Don't think that is possible.
'I'd also like to use free ethernet ports on the TP Link to ethernet from it to some computers to gain internet access through the homeplus connection going through the TP Link wap.' Yes, that will be fine.
You can network the printer if it's connected by USB to a computer that is switched on.