Hello Abhishek.
For question 1:
When you stack switches, one of the switches is chosen as a Master. (Click this link to see how a Master is chosen and how you can affect which one will be chosen. The process is the same for the 3750 and 3850 switches: the http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/71925-cat3750-create-switch-stks.html#anc8). The configuration of the Master including its VLAN configuration will be replicated onto the other switches, making the stack function as one switch. So, any configuration that the other switches may have will be overwritten automatically.
For question 2:
Other than the stack cable you do not require any other connections between the switches. All data communication between switches occurs over the stack cables. Keep in mind that the stack cable goes from switch 1 to switch 2 to switch 3 to… switch N and one more cable goes from switch N to switch 1. (see the link above for related diagrams).
For question 3:
In a sense yes. It is more accurate to say that once the stack is created, you configure the stack as a whole. You no longer worry about the actual location of the config file(s). You just configure THE WHOLE STACK and it does the replication of configurations to all switches for you.
I hope this has been helpful.
Laz