At the moment, you need only your Nintendo Account to play Online, I ditnt tried to play whitout my Account on the Switch so I can’t answer on the Singleplayer..
There should be a payed online service in the next years like PS+ on the Switch, but until then it’s free
My Experience whit the Switch are currently great, the Device my not be that Pocketable like the 3DS or the Pandora, but when you are on the road long enough to play games, then you usually have a backpack (rucksack)
I played hundreds of hours in Handheldmodus and it wasn’t that awefull after all,
The Handheld is pretty heavy because this big screen (and my Battery Pack) but often there is a way to put it on a table or your knees whyle you travel..
The Battery Livetime isn’t long, mybe 3 - 4 Hours, but it’s still amazing for a Device that runs Breath of the Wild, Skyrim or the Farming Simulator..
Speaking of the Farming Simulator: it’s runs much smoother than the 2011 Version on my PC, even whit lots of Machines on the Map, but therefore they disabled one of the important features in a Game where you drive big Farming Maschines: The Mirrors
Par Exempel the Combine Harvesters ditnt have any Way to look behind expect the mirrors, so if you want to connect your Cutting Unit on the Back of your Harvester, to make it easier to drive to a field over a road, you have to use the “third Person Camera”
Ok you could also use a Tractor to move the Cutting Unit but I think most Farmers wants to move it whit the Harvester..
Lots of old Truck Driving Games I have like 18 Wheels of Steel also have Working mirrors..
My Switch ditnt connect to my Fritzbox, only to the Powerlan Adapter , I don’t know why but it’s internet abilities aren’t that great..