Use a systemd-automount in /etc/fstab.
You can add a line like this to /etc/fstab for each thing you want to share:
192.1xx.xxx.xx:/volume1/folder1 /mnt/nas/folder1 nfs x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0