is it necessary to follow what the dealer offers?
or should I just do all the "essential" service, like engine oil, transmission oil, etc.

Thank you.

 

Depends on how long you plan to keep it.

 

Really the only thing that could be optional at 50k miles is the transmission fluid change... note I said change because its only the fluid they are likely to do not the filter....
It won't hurt to do it, particularly if you tow or work your transmission with a lot of stop and go.