Barncat,
the following is advice from someone that has NOT used your version of the board -- so treat any advice as provisional.
On the leftmost panel of VESC-tool there is a menu item for "Firmware" and it looks like that is where you can change the hardware version. But I think V6.0 is the latest so I'm not sure you'll have to switch anything.
I have something similar to a power switch on my board, and yes, in my case it serves as a way of telling the board to activate. Attach a simple switch to those two leads. The microcontroller, and all the functions to run the motor are switched on based on closing the switch. Note that this is not really a _power_ switch -- it does not control all of the voltage from your battery is still coming _into_ the board. You will also get a big popping sound sometimes when you connect the battery leads, regardless if your switch is open or closed, but when plugging in your battery, start with it open.
I am not sure but based on what is labeled on port #7, my guess is the reason they put vBat on there is so an external board could measure the total volts of the battery. I did a 5 minute google search for braking and I didnt see anything. My guess is some throttles work by PPM (there's lots of tutorials if you havent heard about PPM, search on "PPM RC throttle"), and there is probably a way to configure that to do braking. Unfortunately it does not look like it works by using a simple switch.
Based on what I know about the boards you are correct the hall-based throttle would connect to #7, and there is a wizard in vesc-tool to help you configure the board to use it. I dont have much input on the sensorless mode.
The 3.3v/5v selector is probably to set port #3 -- some hall detectors use 3.3, or 5.0, or both.
hope that helps.