First of all, I think you may be confused about what Convoy Routes actually affect. A Sea Zone with a Convoy symbol in it has absolutely NO effect on any naval battle that occurs there. It doesn’t matter if the warring parties have warships, planes or both. A naval battle in a sea zone with a Convoy symbol is just like a naval battle in any other sea zone on the board.
The only effect of a Convoy symbol in a sea zone happens during the collect income phase of the power that controls the territory adjacent to that sea zone and then only if there is one or more warships belonging to a power that is at war with the controlling power.
That being said, I will try to answer your questions. For ease of explanation, I am going to use Sea Zone 109 with United Kingdom and Germany for reference:
1 > This is true. If there is no enemy ships in a Convoy sea zone, then there is no convoy raiding. Since the convoy raiding takes place on UK’s collect income phase, Germany could not simply move a warship into SZ 109 to raid the convoy there because it is not Germany’s turn.
2 > Yes, if you attack a SZ with a Convoy symbol and win the battle, then your remaining warships can raid the convoy on your opponent’s turn. So, say UK has ships in SZ 109, Germany can attack them and if Germany wins, they will control that sea zone. However, on UK’s turn, they could move in warships (if they have them) and attempt to reclaim that sea zone. If UK is successful, then Germany will be unable to convoy raid.
3 > Yes. A convoy symbol has no effect on attacking or defending air units, or any warships for that matter.
4 > Yes. As long as you have a warship (or warships) in the sea zone with a Convoy symbol, you will keep convoy raiding as long as your opponent controls the adjacent territory and he/she doesn’t successfully clear your warship(s) from that sea zone.
5 > Yes.
6 > Correct. If you have a naval battle and clear the sea zone, then launch an amphibious assault and take the adjacent territory, then there would be no convoy raiding. You wouldn’t want to raid your OWN convoy after all.
7 > No. Convoy raid IPCs do NOT affect the National Production Chart. They are subtracted from whatever your opponent collects. Then you take that result, add any national objective money and that is the amount of IPCs your opponent carries over to next round.
EXAMPLE: Say that the United Kingdom is currently at 28 IPCs on the National Production Chart. It is the Collect Income phase for the United Kingdom. Â
Germany has a submarine in SZ 109. Germany rolls 2 dice and gets a 5 and a 3. The 5 is discounted since it is more than 3 (any dice higher than 3 is discounted for convoy damage). So Germany causes convoy raid damage of 3 IPCs to the UK’s income.
So you take 28 IPCs and subtract 3 IPCs leaving the UK with 25 IPCs. Let’s say UK gets no National Objective money this round so the UK carries 25 IPCs into next round.
I hope this answers all your question.