This Skinny Guy's Exercise Goals - Another Challenge

I'm on a mission for health!

Eating better is a good start, but I need to add some muscle...

In my thirties, I'm a little disappointed that I've never made this happen before now!

My Challenge.

My wife and I challenged each other to some physical goals.

The winners get some great prizes, and the loser (if there is one) has to be the driver while we're in Iceland. (An upcoming trip! Yay!)

I want to win!

My Stats.

Below are my current measurements (as of April 20th):

Chest - 36.5"
Belly - 34.5"
Arm - 13.75"
Mid-thigh - 19.5"

Below is what my goal is by September 1st!

Chest - 39.5"
Belly - an 8 pack
Arm - 15.25"
Mid-thigh - 21"

My Thoughts.

I have no idea what is realistic when it comes to exercise. How much can a guy naturally add in size? Is this goal achievable?

Regardless, this is what I'm striving for.

My Plan.

I'm going to start out light, as I'm in terrible shape right now.

For the first couple of weeks, I plan to perform a full body band workout. I'd also better add in some abs - as this goal is going to be tough!!

Depending on how I feel, and the amount of time I can find, I'm going to start P90X (again). Three days a week, then gradually adding in more. I do not think I can reach this goal without some serious commitment!

I have also adjusted my diet slightly.  I've added a few calories (trying to use a calorie app for tracking), lots of protein, and plenty of water!

This is all on top of our backpacking regime (training for a summer backpacking trip). The weekend hikes will not stop!

For fun, we're also in the middle of a 100 day burpee challenge. Ten burpees a day for 100 days! Any extra workouts are good!

I have about 108 days to see where I land...any suggestions?

Yours in exploiting life!
Quinn