The game is full of bots mate. I played for a few years and quit not long after the release of WOD. A lot of people just gave up on the end game grind and turned to bots that utterly ruin the game (PVP especially) for anyone that wants to play legitimately. You'll also miss out on a lot of the old Lore due to the vast majority of the player base having surpassed it. It could be a truly incredible game if Blizzard put half as much effort into maintaining it as they used to.

Not WoW. Pls.

You will have to play through all the expansions. You will have to level up through them. You will need to buy everything, you can't just buy Legion, that's not how expansions work.

Legion is out, WoD is the standard. Everything is free.

Games like WoW are built very high endgame, meaning that there are very few people that play in places that aren't max level. so you can try, but it will probably be rather barren

I would work your first character from the ground up, grind all the way from 1-100 without using a boost to get familiar with the game. First bit of advice, play every class from lvl 1-15 or so before choosing you "main." I can't tell you how many times I regretted hitting max lvl(60 back then) with a tank. I started a hunter shortly after that and barely ever played my main character. After you get your main to lvl 100 I would use the lvl 90 boost on your second favorite character, that gives you 10 lvl a to familiarize yourself with that character then use your lvl 100 boost on your third favorite. Another hint of advice, lvl up your blacksmitching/leather working/tailoring/engineering(whichever you choose). In the end if you have a high level in it you can gain a lot of money by making shit for people. I probably made over 20k gold by making the legendary engineering plane mount. People didn't realize till after I sold it to them that you gotta be an engineer to use it. -blam!-ing idiots. Also, if you're into pvp I would go with the horde. They have out done the alliance since I can remember. If you want to be alliance for pvp I would research a server that has good alliance pvp or it's really a bore to play as you get pub stomped by the horde almost every time. I went with the alliance as I liked the main cities better. I started a horse hunter with a buddy awhile back and playing pvp on him was a lot more enjoyable. That being said the raids are what made the game the most fun to me. People say the new raids are lackluster, I don't have a say in those as I played mostly in vanilla and those raids are by far the most fun to me as there were nearly 6-7 raids to do ranging from 20-40 person raids. Idk what they are now as I haven't played in nearly a year but will be picking it back up once legion comes out. Good luck out there.

Download the client and play for free to level 20 to see if you like it. It doesn't matter if you play the previous raids though, I mean you can do it but it will be dropping gear that will be replaced by quest greens of that level tier. However you might find some cool stuff to transmogrify.