You don't think as clearly in thin air, so even if you aren't high enough to be required to use oxygen, it's unwise to push it.
-----
Don't do formation flying near MCA.
-----
we intend to fly in convoy with some other Cessnas
I've flown in formation before (five planes total), with everyone at an angle to the right and behind the lead aircraft. It gives each pilot a good view forward and to their left of the plane they are following. We were at a healthy distance from each other, but close enough that the lead pilot did all the communications and informed the tower and other controllers how many of us there were.
We picked an unused frequency to talk to each other enroute.
1
...2
......3
.........4
............5
If some engines are more powerful than others, you have to adjust your rate of climb to accommodate the slowest plane.