Welcome
@Nemesis Prime. Pretty much all of us here play single player. This game's core is single player, though there is a massive multiplayer community called Truckers MP, and others. Though no one here at PSF is a part of that. The following info may be overwhelming since there is a lot to read and take in.
The official webforms of the community are SCS Software forums and there is a sizable community on their respective American Truck Simulator Steam forums, or Euro Truck Simulator 2 forums.
Depending on which you want to buy, ATS or ETS2, it is fully up to you. Most people will say buy the base game, and the map DLCs. That is how you get the most bang for your dollar. It expands the driving world/explorable world very fast and is extremely detailed.
For realism, currently ATS has more realistic landscapes and world. The towns and cities are far more realistic to their counterparts as they have really mastered the American layout. But they have recently really been improving the ETS2 world, starting with their Scandinavia upgrades, Italy, Spain, etc. The issue is, they can't capture the density of European countries as well quite yet. American cities (for the most part) are more spread out and the ATS game excels with open countryside. ETS2 releases map DLC usually based on regions, while ATS releases DLC based on entire US States. Even traditionally "boring" States provide an amazing glimpse at rural American life and it really provides a glimpse at how massive driving through America is. So I wouldn't skip and maps if planning to do ATS. Coming next are the maps of Montana and Texas. For ETS2, they are working on the Balkans.
So if you want to go somewhere "Exotic" compared to Finland, ATS may be the game for you. If you want something more recognizable, ETS2 may be for you.
The best time to buy the game and the map DLCS (which they often bundle with deep discounts) is when there is a Steam sale. The game often drops to $4.99USD, so I wouldn't purchase it at full price if you aren't sure if you want it.
The game frequently has updates. All new trucks are free to the game. They frequently update "older" parts of the map to meet their current high standards. They will often include free new roads, routes, and towns and they will come free if you already own a map DLC.
The base game of ETS2 comes with England, Scotland, Benelux, Germany, part of France, part of Switzerland, Austria, Czech Republic, and I am probably missing something, lol. These old parts of the map are not all that detailed but are slowly being upgraded to look like their real life counterparts. This part of the map was made way back in 2012.
The base game of ATS comes with California, Nevada, and is often bundled with Arizona. This is considered the old map of the game, mad in 2015. But it is constantly being upgraded and is currently being rebuilt officially by the studio. They have rebuilt Northern California and are moving south. This part of the map, even the oldest parts, are more detailed and realistic than the base parts of the ETS2 map. In the few year difference, their standards as a studio improved ten-fold as they got more resources.
Today there are two divisions within the development studio. One part works on ETS2 and another works on ATS. The ATS side has a separate division that works on rebuilding and updating the ATS map. The ETS2 team is smaller and has a team that occasionally will work on rebuilding the old map when they have time.
It's a relaxing game, and might be worth a peak. The next Steam sale and big discounts start on June 23 of this year. There is a current sale right now and all the map DLCs are very affordable.
https://store.steampowered.com/app/270880/American_Truck_Simulator/ https://store.steampowered.com/bundle/15571/Pacific_Northwest/< They are currently running two promotions. The Pacific Northwest Bundle is a good one that comes with the base game and 3 map DLCs, plus other content. All their maps are currently on sale and under $4USD.
https://store.steampowered.com/app/227300/Euro_Truck_Simulator_2/ < A decent bundle is also available for ETS2 with the base map and two map DLCs including Scandanavia and all of Poland.