Small anti-TI hint: If you drop really LOTS of smoke, you will effectively limit TI units as well.
As for the machineguns, you may turn them on, limit any opfire to just "danger close" and shoot at enemy tanks just in your turn and just using "W" and "1" to fire only the main gun. That way you have a close-in defense against helicopters and reserve your shots. And I believe in the enhanced op-fire filter in the CD variant of the game it is possible to even limit opfire to aerial threats.
If you want to deny the enemy his air support in campaign, jus go to "Preferences" and set Air Sorties to 0 for his side, or you may input any number to force a limit on him.
As for playing against hi-tech foes, especially well trained ones, as I said, you are pretty screwed, esp. in open terrain. Try to get cities or mountains or whatever. Or try to get worse opponent
(and if you want a real challenge, try pulling off the Golan night battles from 1973, with Shermans or Centurions without any night vision equipment against T-54/55's with NVG
)