this info comes from a Russian video and is based on official info by Wargaming, so it’s very likely correct (unless they change something).
Using individual missions, you will be able to get 4 vehicles in this order: StuG IV, T28 Concept, T55A, Object 260 (it’s not possible to skip straight to Object 260).
As announced earlier, missions are split into 5 branches for each class, 15 missions each. You have to complete 4 out of 5 for each tank (eg. 60 missions for each tank), one branch of your choosing you can skip. Apart from fulfilling the objectives, you also get some reward for each mission (credits and such).
Examples of missions:
First mission for MT branch:
StuG IV: win and deal damage, be in top 10 in XP
T28C: win and deal damage, be in top 5 in XP
T55A: win and deal damage, be in top 3 in XP
Obj260: win and deal damage, be the first in XP
Tenth mission for MT branch:
StuG IV: shoot 6 rounds that deal damage
T28C: shoot 9 rounds that deal damage
T55A: shoot 12 rounds that deal damage
Obj260: shoot 15 rounds that deal damage
Final mission for MT branch:
StuG IV: destroy two enemy TD’s
T28C: destroy three enemy TD’s
T55A: destroy two enemy TD’s that are at least one tier higher than you
Obj260: destroy three enemy TD’s that are at least one tier higher than you
Final Object 260 mission for all branches:
MT: destroy three enemy TD’s that are one tier higher than you
LT: deal 6000 spotting damage
HT: accumulate 14000 damage – either dealt yourself, or blocked by your armor, they add up
TD: deal 8000 damage
Arty: be first in XP and damage in battle
I removed the first IM post, because it SEEMS it contained incorrect information. Hard to say.