I'm using a Vodafone Unlimited Max SIM in a Mikrotik SXT LTE6 but was using it in a TP link MR200 before that.
If you've already got a Vodafone contract already they'll knock £3 a month off and if you talk to the right people they will discount too (like all the providers I assume). I doubt I'm that special to them and they still knocked almost a third off so worth a phonecall.
Hardware wise the MR200 worked ok and proved the idea but if I was buying again I'd get one further up the model range. I ended up with it because I could bring it home from town that day and it solved the immediate problem but I was never 100% happy with it. Whichever router you get assume that the best 4G signal and best place for router location for WiFi are 2 very different places!
Can’t comment directly on the Chateau but my SXT has been very reliable even after I got round to mounting it outside. There is a bit more of a learning curve with the Mikrotik devices but they seem well regarded as routers and are powerful and flexible at the expense of the type of out of the box ease of setup you get with something like the TP Link.
Option 3 is basically what I did but in your case you wouldn’t need a second router just a switch. Stick the 4G router wherever the signal is best and then run a cable to where your NAS drives live. Connect it all together with a switch and fit WiFi of your choice to cover the whole house. As you’ve described yourself as “a network illiterate” I’d steer you away from this option and towards a drop in solution like the MR600.
On the BB speeds in particular - it really is SO location dependent.
We've been moving house over the last year, via a temporary flat, so ...
I tried out the B535 on Three (1 month contract) in two locations. It was mediocre speed (up to 30Mbps / 8 Mbps ish) but crucially was unreliable. stalled connections ie pages not loading. ethernet and wifi. I eventually canceled but didn't raise any issues about box (I'd paid upfront) and kept it
I switched to vodafone and found we got typically 140-150 Mbps, which rarely dropped below 120 Mbps,. and peaked as high as 250 Mbps. Upstream was in the 30-50 Mbps range. Pings about 32ms. Excellent. Same router. We switched to a voxi unlimited sim. Exactly the same.
I then moved location and speeds were erratic. Sometimes 5, sometimes 50. I twigger it was Band 20 kicking in slow so used a tool to disable B20. I managed to get an ok connection, often around 20, but it would still dip below 20, and peak up to 70. Local load and perhaps still flipping bands. The signal levels were weak and there was plenty of CA going on.
Not good enough for work, video calls/voice, but fortunately this was our final stop - new home, so back to fibre broadband...
There's 5G coming on a local antenna so I'm intrigued to see how that may perform in future - but local topology (flat but too many buildings) may mean signal not great either..
So I guess the point is be prepared to try it out. Ensure you take advantage of any trial period/cancelation option.