You can save Johnson by running out with him. You can Faust the Panzer coming up either through the church window; or if you are very brave, by running out quickly and reaching it before it gets to the barrier.
Get a Faust before going to Moody's position. Taking out the tank just when it appears will cause your men to run headlong back to the church. The gate will not come down, and the house and fence will not explode. This often results in them getting slaughtered by the two or three Nazis standing guard.
You can lean from the wall to take out the two MG42S guarding the first flak gun. Doing so will cause a new machine gunner to spawn, but will cause your men to charge forward anyway, leading to a huge pile up of bodies and extra BAR ammunition. Your men will eventually take out the extra gunner.
On the way back, just before you get to the truck, there are three ways to get back to Foley; the alley closest to you, the alley furthermost from you, and the alley in between. You can play around with the alleys and their triggers by running back to the common areas and going down a different alley. By doing this, your men will get caught in a three way crossfire.
In the field at the start of the level, charge forward past the three MG42s in the windows and sandbag. This is best done under the easiest difficulty setting. Stand there without shooting anyone, and your men will waste themselves on the 42s. If this is done long enough and with "insane body count", they will stop spawning all together. You can do the same thing almost everywhere else there is a 42 and spawning men.