I have a small home network which consists of 1 server and 2 clients. This past weekend I downloaded Mandy 9.1 with the intention of upgrading my 3 machines. The thinking I used was to update a client machine with the thought that if something went wrong the rest of the network would still be able to function and then move on to the other client and then finally the server. But, I ran into some problems with the upgrade (it made changes to NFS which the server didn't like). I am wondering, would it have been better to update the server first?

either way doesn't really matter much. With the NFS changes it's likely that it would have broken on either side if you're going half way.

This may be a blessing in disguise. NFS is rather insecure unless you can ensure you're on a secured network. You might want to looking into OpenAFS as a replacement for NFS.