To report back.
I purchased a Peak 4 8m2 two months ago. I have now tried static flying a few times and 3 times on skis. I'm able to go upwind and feel that I can handle the very basics, basically going cross-wind back and forth. I have been pleasantly surprised how fast I can go and still feel safe and totally in control.
I started in very light gusty inland winds just for safety. I guess that was ultimately a good decision but the cost was rather high. I hated the kite at first. I tangled the lines badly, once really - about 5 hours - badly. Also, in light winds the kite with my skill set was just horrible: slow and hard to keep in form. The static wasn't fun either, more than once a gust yanked me and the next moment the wind died with the kite falling down. I think that if I had gone for 5m2 or less I could start with higher winds and it would have saved a lot of my time and frustration.
Now I have had a few sessions in proper winds, maybe 10 - 15 knots. I have also made a system to wrap up the lines and have had zero tangling problems after that. Those two higher winds sessions with skis have been a breeze: zero tangles, fast unpack / pack (about 5 min each) and self-launching/landing has been really easy and felt totally safe.
I think Peak 4 is almost perfect for my original first four priorities:
1. safety first (very important)
2. beginner but enthusiastic / learning orientated
5. upwind: I knew that the Peak is not superb for upwind. I can now - with my little experience - go slight upwind, maybe about 20 - 25 degrees max given optimal conditions. Especially wind speed matters a lot. If wind is too much or too little or varies, the upwind angle goes away fast. I was surprised how fast I lost ground in strong gusts. That was probably mostly due to lack of my skills. But this seems to be the case for the more experienced too. I read that single skins have a higher d/l ratio and that pulls you to the side.
The rest of my list is either obvious or I cannot comment yet. I'm planning to buy a hydrofoil for the summer. With this experience I think I need another type of kite for that. I might be able to use the Peak in water after getting more experience. I think I'll go for a 10m2 used Soul if I manage to find one.
All in all I'm really happy with the Peak. Now I would do two things differently. The first is the size, go small first. The second one is about the packing / unpacking. I watched a few how-to vids before I took the kite out. I should have done more research on this. IMO, the most important thing is to do the landing/packing very carefully and have a system. I now use a couple of clamps I put on the lines before packing.
Thank you for all the commentators who helped me to choose this kite.