Soon-to-be-PS4 owner, a few questions!

A friend of mine asked me and a few other friends if anyone would be interested in gettting his PS4 in the near future, but I have a few doubts on the console as I've always played on PC so far.

Can you guys answer the following questions?

• My last console was a PS2, all needed was the console, the game and that was it; now, I know that you need an internet connection for the PS4 to work and that's fine, but I also heard you need to pay monthly something? Like, to play I'd need the console, the game AND a monthly fee??

• Can I buy games through key sites like Kinguin and such? I've seen a few console keys there but the process seems a bit more difficult, like downloading an account with the game and then being able to use my account to play the game? That doesn't make sense to me!

• How does the whole profile/account/guests thing works? I've played with said friends to PES a few times, and the whole process always seemed a bit complicated to me...

• Memory space, how does that matter? I'd be stuck with his console so it should not be a problem, but what's the difference between the different versions of the console?

• As a PC gamer since ages, I only play with mouse+keyboard except for Dark Souls and sport games, do you think that moving to a permanent PS4 controller on any game would be difficult? Not that I'd plan to play much on that PS4, only the exclusives I can't get for PC...

• Shared accounts? I heard that I can add my account to a friend's one and that way he would share my games, is that really a thing? I'm interested mainly because said friend has invited me to play for years, so it'd be cool to buy the next PES/FIFA and add my account to his so we I can pay for the game, for a change.

Thanks guys, I admit I'm a bit thrilled thinking to own a PS4 soon, I love my PC and I have an high budget gaming monster, but I'm not a masterrrrrrrrace type, it'd be cool to have a PS4 as well!!