My GW7.0.3 server is running OES1. I am looking at upgrading and the
docs don't mention OES1 as a supported platform. I've done some searches
and found some old posts about people trying GW8 on OES1 with mixed
results. So i've decided to back off the GW8 upd until I have the
correct server version.

Reading the docs on OES1 > OES2 upgrade looks rather complicated and
messy. SO i'm wondering if a better option is to setup a new server with
OES2 and migrate the GW7 data to it and replace the current GW server?

Which is the recommended path?

Also, if I do a new server I assume I need to install GW 7.0.3 on it and
migrate users/mail and then upgrade to GW8 rather than migrating data
from GW7 to GW8?