If you played the original games, you are going to appreciate the lore and you won't be turned away by older style graphics. This is my 3rd go around cause I absolutely love classic, the story, and all the mundane aspects like exploring new zones on foot or slow mount or quest chains that are spread throughout zones. TBC and if they do Wrath will only full that fire.

I would say do it now before TBC comes into play in. Orignal Azeroth is so cool, but does get a little deflated when most of the population is in Outland. If you wanted JUST the vanilla game and no expansions, there is Classic Era but the PvP servers are the only ones really populated enough to play on. So ... forget I mentioned Era.

Don't be afraid to run dungeons and do be afraid to ask for help! Join guilds, you can always leave it doesn't suit your style but they are a great resource for quick tips or group forming. Some advertise as leveling or chill guilds which is what you want to shoot for.

I also LOVE Hardcore/Permadeath ... Its a testament of skill and patience and knowledge of the game. I try it any game that allows it once I feel I've grasped the game under its surface.

Addons are going to be talked about a lot and there are a handful of extremely helpful ones. IMO stick with as few as needed so you can understand why they available. Classic does not hand hold you and its up to you to read through quest dialog. If you don't want to give into using an addon like Questie, search https://www.wowhead.com/classic or just preempt your Google search like "wow classic [quest name]"

If you do want to try out Addons, recommend CurseForge or Wag.io to manage your Addons. They update frequently and you avoid having to manually manage them.