yes the motor mounts are suspect at this age, to change them you will need to unbolt the compressor and alternator from the engine - otherwise there is no space to remove or install the mounts, it only sounds big - the job isnt too bad, change the gearbox mount too, its not expensive either.
it would also be wise to check the condition of the atf and the electric connector, if you remove the wiring plug and see oil in it - replace the connector itself with the latest updated genuine mercedes benz spare part only, do not buy any aftermarket part, it will leak in the next hour of install. the diffy oil change is a good idea too - mobil1 gear oil is a good choice.
Another good idea is to drain and refill the cooling system with the old spec mercedes coolant which was BASF glysantin G-05 - it has a service life of 3 years.
The most annoying part of owning the mercedes benz M112 engine is the valve cover breathers, they are the PCV system of this engine and they always leak after a while, remove and reseal them with either threebond 1207B or loctite 5800, Genuine MB sealant, Toyota FIPG or GM engine sealant.
my vote is for GM engine sealant as its gray (cleaner looking) - super tacky and sets up in 20 minutes tops and you will be required to exert herculean strength to undo it. I love this sealant and use it on every repair job. The only downside is that its incredibly thick - meaning your fingers will have an ache, I have a dispensing tool for this too but I usually buy it in caulking tube size and fit that tube in my caulking gun tool.
as usual this model has worn prone lower front ball joints - easy peasy job - repack the wheel bearings while at it - you will remove them anyway. The joints are removed with a 22m spanner and hammer only. Joints are cheap too, lemforder parts are like 15 euros a piece in retail.
flush the brake fluid - inspect it for rotten rubber smell, if it smells rotten then the wheel rubber pipes are most probably shot. replacement time is about 10 years anyway, again very simple job on this car (I love this car because its really easy to work on)
the thing that will annoy you the most is the thumping like sound from the rear when you go over holes n bumps on the road - new shocks wont cure it, the sound is from the subframe hitting the car as the front bushings of it wear out.
there is another set of bushings on this car that are annoying, the front ones in the lower front control arms, like the subframe bushings they are also hydraulic, they are great when new - but have 1 or 2 inches of movement when they are shot - the car will wander or shake at speeds above 100 or 120 - the job isnt simple but again not too hard for a smart technician, spring compressor is required and some tooling to remove and press the bushings.
If you have ownership of a STAR clone then you can test the gearbox for its remaining service life from the adaptation values of the clutch packs, its a scale of 1-9 - 1 = new. I find it very handy in describing the foreseeable service life of the gearbox.