Question 1:
Your understanding is correct.
@rulebook:
Transporting Multinational Forces: Transports
belonging to a friendly power can load and offload
your land units, as long as both powers are at war.
This is a three-step process:
1. You load your land units aboard the friendly
transport on your turn.
2. The transport’s owner moves it (or not) on
that owner’s turn.
3. You offload your land units on your next turn.
Question 2: yes
and
Question 3: no
See
@rulebook:
A quick reaction team of no more than 3 defending
fighters and/or tactical bombers (strategic bombers can’t
scramble) located on each island or coastal territory
that has an operative air base can be scrambled to
defend against attacks in the sea zones adjacent to those
territories. These air units can be scrambled to help
friendly units in adjacent sea zones that have come under
attack. They can also be scrambled to resist amphibious
assaults from adjacent sea zones, whether or not the
territory being assaulted is the territory containing the
air base. They may defend against the enemy ships
conducting the amphibious assault even if friendly ships
are not present. Air units belonging to powers friendly to
the attacked power may be scrambled by their owner if
the owning power is at war with the attacking power, so
long as the limit of 3 total air units is respected.
Question 4 and Question 5:
The British Units can invade Italy during Britain’s turn provided that Italy does not scramble.
@Official:
Scrambling
Q. Say the United Kingdom launches an amphibious assault from a US transport without any
supporting UK sea or air units in the sea zone, and then the defender scrambles. What
happens?
A. In effect, nothing happens. The US transport doesn’t participate in the sea battle because it’s not the
US’s turn. Since there are no attacking sea or air units, there is no sea battle. However, the sea zone
can’t be cleared of defending combat units, so the amphibious assault can’t proceed.