I've been flying with externals on in single player since forever but i don't use them for a practical advantage, it's mainly because i like being able to pause the game, switch to the target and watch the damage model at work, or for looking at the pretty pictures and snapping screenshots
That being said, it does tend to make you pick up bad habits but still, whenever i go online i like to fly without externals/icons. The reason is that while i have an easier time keeping track of the enemy with externals and icons, so do they.
Everyone knows where everyone is at all times and this tends to force gameplay into a series of dogfights, effectively cutting off a big part of the actual engagement: positioning, stalking the target and manipulating the element of surprise to your advantage.
There's more than one ways to skin a cat and i'm all for having extra options to suit everybody so i don't pretend to be superior just for flying with a bit harder difficulty options. I just found out way back in the first IL2 title that flying on a server without externals/icons is actually much easier to get kills because you can surprise people.
The way i see it, if you want to focus on the purely maneuvering aspect of the fight (who is the better stick and all that), flying with externals and icons is the way to go because maneuvering is the entire fight with those settings enabled. If on the other hand you like to be able to surprise your targets and work for the kill in terms of preparation and not maneuvering while accepting that you too will be surprised and shot down by someone you didn't see, flying with cockpit views only is your best bet.
In terms of head tracking now, i was using a trackIR 4 until it stopped working and now i'm using freetrack (same principle but with a webcam and some free software, so it's much cheaper).
My advice is to go for freetrack if you have a webcam and see if it suits you first (some people get dizzy or can't get used to head tracking), then if you like it, you want the extra precision and you are willing to spend the money you can get a trackIR set.
Hope it helps
