New to the Anarduino - starting project, would like advice

I have ordered a couple of the Anarduino units with the RFM69W configuration.

I am doing a project to read digital pins for button presses on one board, and transmit it to the other, where I will in turn duplicate those same pins on the remote end. I'm essentially setting up buttons, that when pressed will simulate button presses on the other board.

A few questions if I may:

I am not sure at this point how many buttons it is possible to setup in this fashion based on what I have read so far. I would like to be able to do 12 to 13 individual buttons if possible, with the possibility of simultaneous presses.

Has anyone seen a reference anywhere to something similar to this that I may examine?

I have read the threads on low power, and how I may improve / test the boards to make this work. Has anyone tried coin cells (perhaps 2 x CR2032s in parallel) to power one of the Anarduinos for intermittent use (perhaps an hour or two of activity per day)? Just trying to work out possible power use as I start trying to design this.

Thank you in advance for any direction or assistance.