Killing it Piros and Guybe,
It will get easier and easier the more you do it. I am not going in much lighter winds on a 1650 foil. The upwind / Downwind thing is interesting and definitely something that comes with practice. Going upwind is easy in comparison to DW. But once you get it, you can pull some decent angles and speeds off the wind. As you'll see above, my tracks upwind and downwind. This was in very light winds.
When I rod the Duotone and Naish back to back I found the Naish to be more powerful (4m vs 4m), mainly because you can get more punch out of your pump. The Luff Strut on the Naish allows the wing to go full depth of the profile instantly and feels sharp and punchy where as the with battens you kind of lose a bit of your pump with the batten soaking up the power before it gets to the full profile (feeling a little spongy) (this is with the boom all the way in/minimum to get more power). The lightwind is also a little easier on the Naish being almost half a kilo lighter so it flies its own weight easier and in less wind plus being physically lighter to hold. (Disclaimer, I am biassed to Naish - Obviously

). Please do not take this paragraph as a brand slagging, just a once off honest feel first try after I had been riding the Naish Wing for about 10 times, so there's likely a lot of getting used to also there.
Agree on trying to get some decent wind. It will help. I don't think it needs to be windy windy, but 12kn is great with a 1650 foil. 15kn you'll be smoking. It's more the annoying winter lulls that will get to you. Once you're comfortable you'll learn to just foil pump through the lulls and can pretty much wing through most gaps.
So much fun!!! Hooked 100% and we haven't even scratched the surface IMHO.
Ride Safe,
JB