The hard starting needs to be addressed.. However on most of the cars when the temps are over 80 they take 6 to 10 sec. of cranking... I would reread the drivers manual and follow it exact.. One often forgets just what it says about that engine and often addresses any normal problems the engine has.. Odds are like Duke said.. leaking injectors.. however there could be lots of other reasons..
110C to 115C on a hot day 90 F or above while setting in traffic or climbing steep grades is not as bad as some will try to make you think.....
Thermostats open full at about 107C or so.. So thats really about 110 for most of us to read on the gage..
Most MB fan clutches come in at 104C to 110C so under about 110ish for most of us the fan clutch is not working..
The electric fans come on at about 100C on low and go to high about 107C to 115C.. so if your car is one of those that runs things in the upper limits 110C to 115C is really where every thing really starts doing what it should..
Above temps are from a Mercedes Factory Manual and cover several models so your should be near those..
In general most of the newer cars tend to run 100C ish to 115C in temps above the upper 80sF... Newer meaning 88 and up...
I would change the Thermostat and change the anti freeze.. Never a bad thing to do any way..
After that you can park the car nose in to a wall so it gets little air flow .. back of garage or side of house on a hot day.. turn the AC on... Roll the windows down so you can hear whats happening... Run the car up to temp at about 2000 to 2500 rpm..
At some where around 100C you should hear the electric fans come on low... about 105C to 110C you should hear the roar of the fan as the fan clutch kicks in... and soon after.. 110C to 115C you should hear the electric fans kick in to high.. ..
If all this happens at temps some where in that area.. Odds are things are normal..
I have no clue why every one thinks their car should run at 80F.. when the thermostats start to open at 85C to 90C.. If your car runs 80ishF it means the thermostat has failed or you have no need for the radiator and fan system as none of the water is going thru it.. Just running thru the engine.. 100C to 115C is normal for a normal working car in warmer temps... and if your car runs under about 90C in 75F plus temps.. Replace the thermostat.. in winter much of the engine cooling is done by the car heater as it is inside the closed engine cooling system and often the thermostat never opens.. thats why the cars will run 80ish C... However in the summer things should start to work normal... 90C to 115 C..