good to see you have found THE most useful site for this style of trip planning.
Your expectations sound ambitious but not necessarily impossible. 90 days is not long for driving around the world.
I am interested to know what vehicle you are planning to use? 4x4 may not be essential, high clearance may not be critical but reliability and proper preparation of vehicle are absolutely essential & critical.
We travelled in our 4x4 vehicle from Istanbul through to Los Angeles in 2007 (last year), we left April 6th and arrived Los Angeles Nov 1st. We did not go via China. We did go via Azerbaijan, caspian sea, Russia, Mongolia and South Korea.
We were joined for some of the time by Motoedde on his faithful BMW, some of the time by a dutch couple with a Lada and some of the time by a French guy in his LandCruiser.
We all travelled similar routes, similar timescales.
We ALL had vehicle problems of one form or another !
You requested info on getting your car to Vladivostok, not impossible but like the China option, very beauracratic and time consuming. I am not aware of any car/4x4 owners that have done it smoothly.
Definately consider going via South Korea IT IS the easiest, quickest, cheapest way.
I agree with HenryUK with regards the ferry, but not wishing to be a 'doom-monger' i also agree with motoedde. The ferry is a freight train transportation route that will squeeze on extra vehicles for bit extra cash. It is easier to squeeze a motorbike on the a car.
In theory there are 2 or 3 ferrys running every day and the crossing takes 12 or so hours. In reality last May we waited 2 days to get on the ferry and then the crossing took 36 hours !
It is not in any way a show stopper for you and i would highly recommend coming through TKM & AZER but be prepared for maybe a day or two waiting at ferry port.
The alternative is via Western Russia avoiding the Stans (no fun atall) or via Iran to get into Turkey (tricky if you have US or UK passport).
Not sure on getting AZ visas in TKM but i would suggest for any visa enquiries to contact David at STANTOURS, they are based in Almaty and know the whole central asia region (and the politics of visas!) intimately.
like most people we've got a website with all sorts of info on there, i suggest looking at the 'coming this way' pages, particularly the txt files.
by the way, once you get the far side of central asia, lets say Istanbul, then what are your plans? do you intend to ship vehilce back to US if so from where?
we are still in US, where are you based ?
enjoy the planning, there's loads of info out there, it's all good ! just takes some sorting through ! everybody experiences these journies in a different way, there is no 'right way' just THE way ! main thing is to get out there n give it a go.
My only advice : Be Prepared, Be Flexible, Enjoy The Journey & remember time is your greatest friend.