On the engine oil Mobil1 is highly regarded.
On the diff oil, it's 80W90, if you want to find a synthetic, it would be OK, but I don't think it matters.
On the trans, i would only use a name brand MerconIII/Dexron, I wouldn't experimant with synthetics in it, especially at this mileage.
On the dash, there is no speedo cable, it's electronic. You need a pair of cluster pulling rods. I think they sell them here at PartsShop or Fastlane.
In the cooler times in S Florida I would assume you'd run an engine temps in the low 80's (celcius), in the summer you may see 90. Much above that for extended periods and I would suspect either a bad thermostat, plugged/dirty radiator, or an inop aux fan system.
The REST button is pushed after shutting off the car. i think it's mostly intended for cold areas. It runs the heater fan at a low speed to help maintain cabin temp for short periods. It may work for hot climates (using the temp in the evaporator case) but I think it mainly is designed to use the heat in the heater core, as it also circulates coolant through the heater core when in operation. The REST function will time out or shut itself off if the battery voltage gets too low.
I think the best source for the owners manual is direct from MB. Just call the 1 800 FOR MERCedes number and you want to talk
to someone about technical literature.