Going off what CP said... In my opinion, if you have up enough interceptors to where they can't drain the helos, you don't need that many helo wings.
If you have 80K interceptors, and 40K helos, that takes a lot of manpower. Most people will come in to take out interceptors first then drain the helos. If I had at least three countries with fedded air defense, with 80K interceptors in each, you won't need many interceptor wings, maybe 20K for all 3 countries total. You can keep extra interceptors on hand to replenish or redeploy more air wings and most likely if the attacker can't take out the air defence, those helo's would never see action unless the attacker is willing and capable of taking catastrophic losses. It is rare to see a single player take out air defense quickly.
You need to be fluid with air defense, templates are useful but you'll need to adapt them to your situation. The most pertinent factor in evaluating your needs will be "What war level are you playing?"
If your answer is 0 - 2, then you need nothing but a few helicopter wings and a good amount of ammo to prevent and discourage sneak attacks.
If your answer is level 3 or higher, you'll need more for a good country, you'll need a monster amount of air defense to deter potential attackers.
And as far as this...
<!-Quote-!>Quote:Make sure every city has a nuclear defence battery and 20 or so ND missiles (in the form of a garrison blueprint).<!-/Quote-!>
That is okaaaaay advice, if you'd go so far as to call it that. You'll need
2 nuclear defense batteries and they need be of good quality, or I'll still nuke you. Cuz, yes, I have just that many damn nukes and bombers...
Note: the ammo for the nuke batteries needs to be of high quality, the jeeps you also want to put in the garrison for forts per matts suggestion also need be of high quality, or they'll drag the garrison quality down, then I'll still be able to nuke you. You also need to keep those supply units, and make sure you buy the appropriate upgrades to make sure those high quality weapons don't degrade, and I nuke you some more. Also, if you are war level 0 - 2, you don't need anything but the few helo wings to keep sneak attackers at bay.