When a jinchuuriki goes into version 2 mode, the number of tails that they have can be different from the number of tails their tailed beast has. For example, Naruto, the 9-tail jinchurriki, only had 6 tails in his fight against Pain. My question is does the user have to start at 1 tail and move his/her way up? Can they have more tails than their tailed beast has(6-tail jinchurriki getting 9 tails in version 2 mode)? Also, can the user control how many tails they have or are they not in control anymore in version 2? I ask this because Naruto seems out of control in this mode(hitting teammates like Sakura that one time).
Does the user have to start at 1 tail and move his/her way up?
No, they do not need to work their way up from 1 tails. As we see in this youtube video, we see Killer Bee transform directly into 8-Tailed Version
Can they have more tails than their tailed beast has?
Plausible, but why would it? According to Jinchūriki Forms wiki, we mostly see version 2 only having the same number of tails based off of the tailed beast, but there does not seem to be any reason how the 1-tailed would be able to have a 9-tailed form
Most jinchūriki have only been seen to enter a Version 2 state with the same number of tails as their corresponding beast
Naruto is the only Jinchūriki we see that contains different number of tails
Naruto is also an exception, for he has only been seen in a Version 2 state with four and six tails (and seven tails in the anime)
Also, can the user control how many tails they have or are they not in control anymore in version 2?
This depends on who is on control and if the Jinchūriki and Tailed Beast are in unison . The reason why he attacked Sakura while in version 2 is because, at the time, he and Kurama were not in unison
As the seal that kept Kurama contained weakened over the years, he became increasingly susceptible to its influence. By fully submitting to the beast and his own rage, Naruto would grant Kurama full control of his body who then formed a Version 2 shroud around him. Naruto's ability to distinguish between friend and foe vanishes and he attacks in whatever way will enable him to defeat his target, oblivious to the consequences of the attack
In multiple instances, Killer Bee is able to enter in Version 2 and maintain the ability to determine friend and foe due to him and Eight Tails being in unison