*Its a little long and if I didn't explain something well enough let me know. Or if something is redundant *
No one can tell you how to have fun, just do whatever is fun for you. Leveling as fast as you can? go ahead, Do you want to experience the quests for the first time without being told where to go? Then after an hour getting frustrated that you still cant find Mankrik's wife. I found that fun, not being told where to go and having to figure it out my self or eventually giving up and looking it up.
My earliest memory of WoW that I can remember was when someone first showed it to me a few months after it came out. I played a night elf and after an hour in the game probably still only level 2 or 3 I died and had no idea how to find my body. So I just made a new character. leveling fast going hardcore raiding in a guild didn't matter to me, I just had fun playing the game. What I mostly did was just run around doing quest killings things and talking to people.
Now i'm definitely not as bad as when I first started, and neither is everyone else so I'm curious how it'll go. Especially since a lot of people are use to Modern WoW as it is.
But as for what class your friend should play? There's a lot more information out there then there was when WoW first came out. He
could take a look at what the classes offer and see which one he would like to play but try not to pick which ones that are perceived to be the "best". They could be the best at what they do but if you don't have fun playing them then whats the point? Why play a game like a job? Play to have fun. If you want to experience Classic WoW blind go ahead I find it fun going into a game with no information and to figure it out myself but it might be different for you. You can also look up how to play the classes perfectly the best strats to level before the game comes out if that's how you wan't to play then that's how you want to play.
As for addon's? again that's up to you guys. There's DPS charts there's that questie addon thats shows you were to go I believe. There's Meter addon's for dps/healing but those don't really matter for leveling. I havn't really looked at the addons since I don't plan to use them, but look at the addons see if there's anything you want to use.
As for a think of it like a high school, you join a class that has the serious students that are focused on scoring an A+ and being perfect. Now that's fun for them but you see a classroom down the hall that's getting d's-c's who don't care that they're almost failing, that they're wiping for hours on a boss or that some people are getting f's. While the teachers just playing movies and having fun with them instead of teaching, and you're jealous that they're having a blast while your stuck in the quiet room where everyone has to be perfect at all times. If you guys have fun in the A+ perfect class then join that class. Or if you don't care that you're not clearing the raids in the first day or even the first 3 weeks, then join the fun class. Its all up to you guys on what community you want to join.
TL:DR No one can tell you how to have fun. Figure out the way you want to play and just go for it. Hardcore rush to the end? join the A+ Class . Just have a blast playing? join the Guilds for the people not the performance and just play the game. However if you want to be serious about raiding also don't join the guilds that refuse to deal with people that are obviously the issue to not killing a boss.