[Mobhack]

1) yes

2) gaps are best at the end. otherwise the formation throws a "line break" and splits into 2 or more sub-formations. The above may well have a co HQ on its own, and 3 platoons. Only testing could tell you.

Section
section
section
APC
APC
APC
Inf-SAM (later to end)

In the demonstrated platoon, the inf-SAM is available later on in the era of the formation. Since it is at the end of the list it works. If it had been tacked onto the infantry sections then there would be a break at the APCs when in the early era and the SAM was not there.

There is plenty one can do with formations, there are no written down rules, you will need to experiment and test thoroughly if you are trying "special effects".