Your questions seemed a bit complicated to answer but I see you edited your post which makes it a bit easier to provide some advice.
1. You can use the Mobius Maxi or you could use the original Mobius 1. The original M1 will be more reliable as many unresolved issues still remain with the Maxi. Still, the Maxi should be fine if you choose to go with it, just expect you could have a few issues now and again.
2. Yes, go with the 5.0 Megapixel Varifocal from Treeye. They would be my recommended vendor so you've picked a good seller. For dash cam purposes you want the one with the IR filter.
To answer your question, yes, you will need to adjust and focus the varifocal lens to your requirements. The two knurled rods on the side of the lens are for adjusting the zoom and focus. Once you put the lens on your Mobius, plug the camera into a USB port on your computer and open the image in "web cam mode". This will allow you to zoom and focus. (See the Mobius owners manual for web cam mode instructions.)
3. Depending on your requirements go with either the 10 foot or 15 foot Monoprice USB-A to mini-B - 28/24AWG cable. They also offer a 28/28AWG cable but I'd recommend the thicker heavier wire gauge one with the ferrite bead.
https://www.monoprice.com/product?p_id=5447
4. Any good quality USB car charger should work fine. Just make sure it outputs at least 2 amps per port.
https://www.amazon.com/car-charger-dual-usb/s?k=car+charger+dual+usb
5. For a mount I would recommend one of the following or similar. If you look around on AliExpress, eBay and elsewhere you may find them for less than on Amazon but this is what they look like. For my Mobius M1 set-up I use the mount in the first image but the second one may be more flexible to use depending on the slope of your windshield.
View attachment 55822
View attachment 55823
https://www.amazon.com/gp/B00BPRLNQ2
https://www.amazon.com/gp/B00QSFKJ8E