Intiatiative determines who gets to make the first attack. After that attack is resolved the other player gets an oppurtunity to attack or pass.
If they pass it is back to the first player to pass or attack. If they attack, resolve the attack, and again the first player may attack or pass.
Repeat until both players pass consecutively. This takes care of your question 3.
As to addresses when you run out of units take the dice that hit and start at 1 again.
So for four units defending (2 Inf and 2 Arm for example.) The 1st INF is subject to hits from rolls of 1 and 5 and the 2nd INF is subject to hits from rolls of 2 and 6. The Arm can only be hit with 3 and 4.
If there were 2 INF and 3 ARM the first INF would be hit on rolls of 1 and 6 while the other Inf only gets hit on 2 and the a ARM would get hit on 3, 4 and 5. See this thread for an earlier explanation. But it doesn't really go into wraparound which is what you are asking about.
When there are more than six units defending you have to re-roll the dice that hit (all the 6 or less results from the total attack dice) in order to determine the addresses. Say 4 INF, and 3 ARM. Your INF would each be subject to hits from 2 results-- 1 & 8; 2 & 9; 3 & 10; 4 & 11. While one tank would be subject to two results 5 & 12 and the other only to 6 and 7.
Again this would be after rolling the total attack dice and determing the number of results of 6 or less.
Look's like Krieg beat me to it.