For the ABS you probably have a dirty speed sensor or a problem with one of them at the wheels....clean/inspect each one. It might be skipping the self test and just putting the light on, but holding the pedal like you said might be tricking it into a successful self test. (The self test is supposed to happen and is normal to shudder slightly)
Not sure on the suspension thing, but the self leveling does take a moment to compensate I believe, so it may still squat a bit on heavy acceleration....might be normal. Fluid level must be kept proper and checked. Don't let it run dry/low!  And ONLY USE MB SELF LEVELING FLUID from the dealer! I'd check/top it off ASAP. Make sure there are no leaks in the system.
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