Hi, thanks a lot for all your replies. I really appreciate that my post wasn't just taken as a rant from a disgruntled new user, but as constructive criticism from a different perspective.
I'd like to address some points made. Please keep in mind that all this is from my own personal experience. I can't claim that it's universal, but just some subjective observations from one guy who tried MySensors. That said -
@BearWithBeard I have to respectfully disagree about the guides being generally fine. Yes, they are nicely written and well presented. They're very inviting for new users. That's important and sets MySensors apart from many other open projects which often look very unwelcoming to new users with very steep learning curves. Having been involved in a few FOSS projects, god knows I have been guilty of that myself. The problem with the guides is the information contained in them. It's outdated and misleading.
From what I could gather on the forums and also from replies here (as the one from bjacobse), is that there are a number of best practices to follow with a MySensors project. And you have to follow them closely. If you don't, you will inevitably run into problems. Don't use the ENC28J60 network chip, it won't work. Don't use the NRF24L01+ if you want a reliable connection. Use external voltage regulators. OK that's all fair. But while these practices seem to be very well known by the community, even taken for granted, they are not documented for new users. In fact, the very guides written to draw new users to the platform will actively encourage bad practices - by presenting them as perfectly valid options.
Yes the information is out there somewhere. But it's often hard to find, spread out and riddled with confusing and conflicting (and sometimes plain wrong) info, sidetracking you.
I'm also not that sure if my choice of hardware is so unusual. Maybe people selecting such HW will simply never show up on your radar, because they give up early on due to all the problems they run into.
For the network chip, yeah, it's not widely used on Arduino. Yet the ENC28J60 is not uncommon for giving RPi Zeros an ethernet port. Like most of these cheap Chinese modules they're usually sold in packs, so probably more than one newcomer to MySensors will have such a module lying around in a drawer somewhere. Especially if he comes from the RPi community. Your starting guides make it sound like this module is a perfectly fine choice. You just have to install these libs that MySensors specifically modified for it (but they were never updated and don't work with the new AVR stuff anymore), and you're good to go ! Well no. And then later on, after hours of frustration, you find a forum thread where mods openly say that the ENC is unstable, untested and should be avoided, then reading the guide sounds almost cynical to me. If something is known not to work for years, then remove it as an option from the newbie guides. Having only one single network chip class supported (the w5x00 line) is perfectly fine. Just don't mislead people into using unsupported HW.
The NRF24 situation is similar. I understand that historically this was the only supported radio. I also understand that it is again unwritten community knowledge that mostly due to the market being submerged by barely functional Chinese clones, there's a good chance the performance with this module will be abysmal. And also that the RFM69(HW) is a much better and more stable choice for many use cases. Yet, this is not mentioned anywhere in the newbie guides. The NRF24 is still presented as the primary and default choice of a radio. With an image of a cheapo Chinese clone module right next to it. I think your idea of adding the pros and cons of each radio would be tremendously helpful when starting out. Had I known the issues with the NRF clones, I would have either ordered a better nRF based module (like the one from Sparkfun) or something RFM69 based, before even starting. And this would have saved me from a big disappointment later on.
Also, please don't underestimate the number of users coming to MySensors from the RPi communities. A lot of DYI home automation people use controllers like Domoticz, Home Assistant or similar running on a Pi. I'm sure that many of your own established community members also do. It only makes sense for many to install the MySensors gateway directly on their Pi. And that's where people will inevitably run into issues like I mentioned in my OP. If you browse the forums from these communities, when people ask about creating their own IoT devices, they will more often than not be pointed to the ESP8266 / NodeCMU stuff running on Wifi. With the result that all their DIY IoT devices are directly connected to a public IP network, with all the fun and not so fun consequences this can have. MySensors would be a perfect and safe alternative here. But I can't stress this enough from my personal experience, having the newbie guides be up to date, working and promoting best practices is absolutely primordial here. They're the first contact people will have with MySensors. And not everybody will have the persistence to keep going through the rough to try to make it work. Many will probably just give up and turn to things like the ESP.
@bjacobse, I appreciate your comments and advise. I have a running ethernet GW at this point, albeit with very unreliable radio link. A serial GW was not an option due to the way my current HA infrastructure is laid out, which is an entirely Ethernet based internal IoT subnet. Your comments about best practices with the ENC and the NRF are spot on and should be made more clear to newcomers.
Again, please don't see this as a direct attack on the MySensors project. I think it's a great idea and a lot of awesome work has been put into it. But communication is really important for new users. And please also think about the type of user who is 'only' looking for a working and stable base platform he can build sensors on. For these type of users a known stable setup, both HW and SW wise, should be recommended in my opinion. Along with best practices and pros and cons for HW with valid options (like the radios).