I'll try to cover all your questions:
1) Use an Ethernet cable for convenience. A USB or PCMCIA adapter would be possible if you have one lying around, but installing its device driver might not be acceptable if the laptop was provided by his employer.
2) You will normally need to add a permission to the laptop's client firewall to use the LAN, and you may need to a rule in the printer host's firewall to accept printer traffic from the new client.
3) Yes, it will need to join the workgroup if printer sharing will be utilised.