Hi. So I did it by motorcycle, Yamaha WR250R. I rode from UK to Japan via central asia largely via backroads and trails. My Asian route for that section was Turkey > Georgia > Russia > Khazakstan > > Uzbekistan > Tajikistan > Kygyzstan > Khazakstan > Russia > Mongolia > Russia then some ferry services to Korea, Japan, and on to USA etc.

Few things to note: 

There are always travellers passing through the Pamirs. 99% are following the main "Pamir Highway" route which is passable by all normal vehicles. The vast majority are travelling Eastbound, but you will see a few coming back the other way. Facebook is a great place to find traveller groups who are setting off at various dates. Or you can just meet fellow travellers at the camps along the way. The main route is a veey well beaten path and there are many tourists, accomodations, yurt camps etc. I didnt plan to travel with anyone, but ended up meeting a selection of people and at one point I was travelling in a group of 10 bikers of various capabilities. The bigger bikes and cars were stuck to the highway. Enduros took the higher roads were there no tourist services at all. Literally nothing. If you break down away from the main route, you are stuck bad.

Dushanbe is kind of the best hub from which to organise anything like spare parts, repairs, or meeting up with fellow travellers and hang out for a bit. Its a cool town actually and a great plave to break up the trip. There are ztorgae facilities there and many people leave there vehicle there and fly back in to continue.

Western Uzbekistan has long stretches of desolate desert with little facilities and poor quality fuel. Plan accordingly and really make sure you are equipped for a breakdown passing that area. Also the border process at Uzbekistan can be comically slow. Arrive early. It took some people 10+ hours to cross. We paid a small bribe and were through in less than 1 hour.

Khazakstan still has problems with roadside corruption and regardless of what you hear, cops may still find reasons to pull you over in a foreign plate vehicle if you look like an overland rig and stick out from the crowd. You can refuse to pay, but they will make your day slow and annoying. Eventually I just removed my licence plate refused to pull over for them, they didnt follow in rural areas, but city cops will chase you down lol.

Understand the limits of your vehicle in the Pamirs. The primary routes are actually well maintained and most local vehicles are just small regular FWD family cars. However, if you choose to leave the main routes and try for mountain passes then the road conditions deteriorate rapidly. I got by because my trail weight was about 130kg for the bike and I could bump it over steps and ruts. Many of those routes would be completely impassable by car including larger 4x4. 

Account for how your vehicle will operate at altutide if you plan to take mountain passes, some of those high routes cross 4500m and your vehucle will be operating in conditions for which it was probably not designed. On that note, make sure you know how your own body will react to altitude. Ive seen tourists be evacuated from the roadside rest stop at Ak Baital something like ~4400m. 

Pack lots of spare fuel filters and use them regularly. Bring an external fuel filter sock. Bring quality oil with you to plan ahead for servicing. 

Visas can be problems. It took me 3 weeks to get my Uzbeki visa in Turkey. Russian situation is difficult now so I assume you may have to take Caspian ferry route. Not sure how you woukd leave the other side though, unless you did Karakoram escort and went Southeast via Pakistan. I know someone who did that but it was thousands in fees and permits.