There are varying levels of code on the github site. All of the code can be used on a MEGA and I really would recommend it. I originally did the nano because I was going to put it in the wand but ran out of time and just stuck it in the pack. I would highly recommend anyone starting out now just use the mega as you can easily expand on it and the nano is down to one pin I think free.
https://github.com/CountDeMonet/Arduino ... itMinimial - This one is the bare minimum that I threw together for my spirit pack. Just powercell and cyclotron and meant to be a simple project for someone with little electronic experience.
https://github.com/CountDeMonet/Arduino ... trino_Wand - This is the one currently on my pack. Fully controllable with just the sound board and arduino and the base for the next two. You can start with this one and then move up to the next set of code to add the sx1509 later.
https://github.com/CountDeMonet/Arduino ... With_Graph - Adds in the sx-1509 for the bar graph. If using a mega though you could skip the 1509 if you wanted to. Would require a little code change to not use it and address the mega pins for the lights. One benefit though regardless of nano/mega using the 1509 is less wires having to go to the wand.
https://github.com/CountDeMonet/Arduino ... ECig_Relay - This is the big daddy with everything and the relay code for the ecig venting.
The first two will work with partial components connected. On the one with the audio board you will find the code runs slower if the audio board is not connected though. You can get around that by commenting out the contents of the play function until you have it added. The other two require the sx1509 to be connected or they will halt
Which buck converters are you using? Is it the one I recommend? If so there is a little pot on it that can adjust the voltage. Doesn't take much movement to do that adjustment so definitely test with a multi meter
Rumble motor could be implemented utilizing another relay to turn the motor on and off just like the ecig. You would want to figure out when you want it to rumble and turn it on and off with those features. If you wanted variable speed rumble you would need to add a motor controller which makes it more complex but still doable.