Zaanse Schans-Edam

No, I believe you have to take the RNET 817. Per their website

"The Rnet-bus 391 runs from Amsterdam Central Station every fifteen minutes to the Zaanse Schans. The trip takes forty minutes. For more information: www.bus391.nl.
The Rnet-bus 817 drives in July and August from the Zaanse Schans to Volendam/Edam. Also in the weekends Ascension Day and Pentecost is the bus available. For more information: www.bus817.nl."

If the website comes up in Dutch, go to the upper right corner, click on the down arrow next to NL and select EN for English.

At central station, get the platform information from the automated boards. When we went last summer, the information office had a.a if with one platform for the 391, but the boards down at the platform had the correct one.

To the best of my knowledge you indeed have to take the bus to Edam from Amsterdam Centraal station.
Check the connections at 9292.nl shortly before your intended trip. Public transport will be effected by the corona crisis, and it is impossible to say how it will be arranged in an unknown period of social distancing, which in the Netherlands is already called the "1,5-metre economy".

Thank you both for your input.
I have been using 9292 this afternoon working out other areas to visit. Very useful, thank you.

Thank you Stephen- just looking into the region travel tickets. Does this ticket also work for the bus
to the Keukenhof gardens or is this a separate?

Sorry I meant Stephan.

We have toured the windmills twice but on the second visit out there was no wind so the windmills were not running.