Technically their is only 2 versions, dex210v1 and v2. The great thing about Durango is v2 parts can be directly attached to the v1 without mods so some racers have a mixture of v1 and v2, like myself.
Here is v2 parts that are most notably difference:
http://www.amain.com/team-durango-hd...-arm-2/p296476
http://www.amain.com/team-durango-sh...type-b/p298932
v1 parts:
http://www.amain.com/team-durango-fr...-set-2/p213146
http://www.amain.com/team-durango-sh...er-set/p213151
The difference between the arms is the v2 are solid vs v1 are gull winged and open. The difference between towers is the v2 is lower vs v1 are taller.
I only have one recommended upgrades and it is these:
http://www.amain.com/team-durango-14...-red-2/p274295
Here is a great site for team builds, manuals, gearing, upgrades and more.
http://durangofansite.com/main.php?v...ket&itemid=104
Second hand items and be just fine. Just make sure to replace any wobbly parts, stripped screws and any thing else that looks not right. Having the manual next to you works great.