My experience after using HA for around 4 years:
1.) This is a good overview of the install methods and respective skill level etc.
I would not suggest using Home Assistant Core (in a virtual env) unless you really know your linux and virtual environments, python etc. Personally I use Home Assistant Container as it gives me the flexibility to run my “own” docker containers for which no add-on exists or the add-on is not up-to-date. In addition I can install my own stuff on the host system, which is not possible/limited with Home Assistant OS.
2.) Depends on what you are doing, NVR or AI stuff may sometimes be better to be on separate hardware (like a Google Coral stick for AI).
I put my Z-Wave and ZigBee stick on a separate Pi, because the NUC running HA etc. is inside a rack where the range is limited.
3.) Dependa on what you want to do with the data. I use Postgres and keep data there for 7 days for the logbook and history and for long-term data I use a separate InfluxDB and Grafana to make some nice graphs etc.
4.) This you should do anyway, even if your hardware is powerful enough. Why would you want to keep history of the sun elevation or the time?
5.) The native automations are enough, I haven’t found anything that’s not possible with native automations yet. And in my opinion Node-Red is just an unnecessary additional layer, however if you are a graphical guy Node-Red is a good fit.
6.) What’s next level for you? What do you want to know? In general I just read up on individual topics that I’m interested in, then I start to implememt it in my system and then read more and more.
7.) I like to take a look at github repos from other experienced people to get new ideas for automations, hardware and software to use.