You could use fig 4.21 for semi-automatic (hand-held) SAW but I would make the plates longer than the 5" minimum.
For automatic (machine) SAW use fig. 4.22. Again, I would make the plates longer than the 15" minimum.
Your parameters should be in accordance with your WPS. However, SAW is a prequalified process, so for your WPS you can choose whatever parameters work best for the testing, as long as you are within manufacturer's recommendations. I would make up extra test plates and have your welders give them a go. If you have difficulties, make some adjustments, and make sure your WPS covers the new parameters. Then weld out your test plates.
Chet Guilford