Toe-in is most critical to the tire wear and how the car drives. Ideally, you want the front tires exactly parallel when driving. Because of play, the tires toe outward from the driving force. You want to set slight toe-in to counter that. BTW, FWD cars set slight toe-out since those tires pull and toe inward when driving. The M-B manual wants you to push the tires in toe-out direction w/ spreader bar, to simulate the driving condition and take out most play. The remaining toe-in they spec probably intends to account for later wear of steering joints and sag in the springs. U.S. cars with similar steering setup don't spec a spreader bar, so probably not essential, just allow another 1/16" for play, assuming your parts are tight.

I measure toe-in w/ a tape measure, subtracting AFT - FWD distances across the 2 tires. My tires have straight channels which make this easier. You also want to adjust so the steering wheel is straight while driving, which often takes a little trial and error. You will see that even 1/8 turn of the adjuster is easily noticed on the tape measure, so I wonder how a laser machine can do better. Indeed, former techs say they would sometimes bump the wheels and jigger the machine until all showed in spec, then print the report, i.e. cheat a bit, so might not be any better. A good final check is to hold the level against the front wheel and sight at the rear wheel. It should fall ~1" off the rear wheel on both sides (FWD is easier since view line falls on the rear wheel). If not equal, drive forward to center the wheels first. Drive the car around the block and measure again since may shift slightly. If steering wheel is cocked when driving straight on a road w/ slight camber, turn adjusters the same amount in opposite adjustments and try again. Think hard which was to turn them. You can actually see the wheel move as you turn slightly.

For camber, I hold a 4' carpenters level vertical, resting against the fender at the top and slide the bottom until perfectly vertical, then measure from level to rim at top & bottom. You want the top leaning in slightly (~1/16"), meaning "negative camber" to give better cornering, w/o excessive tire wear. Indy cars are set w/ extreme neg camber. It is more of a personal choice than exact spec. Set 0 camber for the least tire wear. Some older cars set slight positive camber (tires leaning out).

I never worry about caster, but would if I replaced the guide rod mount. In many cars, it is not even adjustable. Caster is where the line between centers of upper and lower ball joints projects onto the road. It should fall slightly in front of the center of the tire contact patch. Caster is the "shopping cart" effect where the wheels will try to follow the direction of car motion. In my 1960's Mopars, one strives for the most caster possible since the steering was designed for bias-ply tires which don't deflect as much as today's radials. We use offset bushings to get there.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans