Use 16.3 Lite since it may be a while. You will still have some of the newer software that is back-ported by Zorin and you have Flatpaks and Snaps for other software. Then when ZOS 17 Lite comes out and after the upgrade too comes out, you can upgrade. Or you can do a fresh installation. Up to you.
I can't give you an answer as to when ZOS 17 Lite will come out but it seems it will take from a few weeks to a few months. That is why I say just install the 16.3 Lite version which is still very much current and supported. Xfce has not changed much so I can't see big changes in ZOS 17 Lite but I am sure there will be all the special sauce that Zorin puts into their distributions.
I have mentioned other similar distributions ranging from antiX to MX Linux to Linux Mint Xfce to Linux Lite. I have read a lot of Bodhi Linux being very light on resources but have never used it.
Good luck!