With FC2 you get A LOT of activations... (8ish?).
If you waste them all, legit, you've got some serious hardware/software problem/fetish.
When FC was the latest, I got a faulty harddrive 3 times in a row and ran out of activations (because I didn't know how to properly save them).
I mailed ED about it and got a new one.
Fast and easy. No questions asked. I've had the game for quite a while then aswell so maybe it added to my credibility, who knows.
Bottom line - with ED, you're in good hands :)
It might be good to scout the actual area well beyond their fire envelope. Fly slow and check with the IR seeker where you have targets (the higher altitude the better, but in the campaign you're pretty much limited to ~2600ft. Make out which targets are threats to you (AAA, IR launchers), remember the location, turn around, engage one unit and repeat.
It takes a lot of patience and consumes a lot of time, but in the end you'll most likely make it.
I can also recommend to pause the simulation when you have aquired a target by IR and see what it actually resembles. Then press F7 and cycle 'til you hit gold :)
If supply trucks are nearby they reload within a certain time limit. The time limit is mentioned for some units in the encyclopedia. For example, the KUB 2P25 LN takes 10 minutes to reload.
They update automatically but you have to be in NAV mode.
As for the diamond. I think it's the wingman that calls them out and sets them on the biggest threat. When you fly the A-10 campaign you'll notice it's always set at the SAM sites.
You have to spot the targets for yourself :)
Go to controls, select mouse (i think), select "axis", select thrust, click change, select mouse2 (again, i think... there should be mouse0, mouse1, mouse2) from the list, press ok.