Way to go on the new toy! Congratulations on the find!!!
Re the exterior indicator light, another thing to check is that all the pairs of bulbs are of the same wattage. As example, the left and right tail light bulbs want to be the same wattage. It is a good idea, as JCE suggested to be sure they are of the same (preferably OEM) manufacturer as well. My Porsche had this same problem, which turned out to be due to two seemingly identical bulbs, but from different manufacturers. Tossed them and replaced both and no more problem (and the replacements were substantially brighter, being some 12 years or so newer)!
The shaking engine at idle could also be due to carbon build up. Perhaps you can run a bottle of Red Line fuel treatment and go for a long ride…
'00 ML320 "Casper"
'92 400E "Stella"