There are a load of OH supported devices available that will do most of what you want (not sure about 10 speed settings though). Most are based on some form of wireless control for easy installation in a typical house. I use both ZWave (low power mesh network) and WiFi (Hue lights, Sonos) but there are others too. Sensors (PIR, temp, light, smoke, humidity) are usually battery powered and control units (power sockets, light switches, heating demand control units) are typically mains powered. One exception I have is a battery powered Zwave TRV valve for my radiators, which I use to control heat in each room independently.
I suspect you’ll want a hybrid and to run off-grid without an invertor you’ll probably need to look for a DC powered relay or make one yourself to control your heating.
Before I used openHAB I had a hard-wired system I designed myself (both the software and electronics), using a Velleman K8055 USB board as the base. It’s old now and probably obsolete but it used a PC running XP and Visual Basic to control a set of digital and analogue I/O ports, to which I added thermometers via the onboard A/D converters and relays to control heating demand. It worked but it was a pain to install, build and program. There is an OH binding for the Velleman board but I could never get it working. OpenHAB is way better than my old system but you need to list what you want to monitor and control and check what devices are available to do the job for you.
Take a look at the list of Bindings in openHAB – that will show you exactly what you can interact with using openHAB and may give you some inspiration too.
A word of caution – battery powered devices (Zwave at least) try to minimise battery usage so effectively “go to sleep” most of the time and any commands you send get queued up until the device next “wakes up”. You can usually set a “Wake-Up” interval but for things like PIR detectors it may be as much as 30 minutes before they will send say a temperature report, though they will report immediately if a PIR sensor is triggered.
They all have their quirks and it’s best to read up in detail on their manuals before you buy to make sure they will fit your purpose. Lots of people have posted on them too, asking and receiving good advice about them.
I’d also suggest tinkering with OH on a PC before you go Pi. There’s quite a lot to learn and it just makes the learning curve a bit less steep to begin with.
Oh and it’s worth always having a manual control for when you get a bug in your code or Windows decides to do an update or something else goes wrong. I don’t think the community has quite cracked “high-availability” yet.
It sounds like an interesting project.
I’d be interested to hear how you get on, particularly with heating control and web-cams as I may go that route myself with my caravan, though I doubt I’d get it working off-grid as it’d just be too much hassle for a lazy bloke like me. “Laziness is the mother of invention ”