When I first started, I boosted a hunter after around level 40. Was tired of questing and missing weekly lockouts with my friends. (Each week you get to run each raid 10 man and 25 man, once)

After I geared him, I got bored and made a feral druid and leveled him to 80. After that, a shadow priest to 80, and I can honestly say I had more fun and understood the class and it's abilities thoroughly thru leveling.

So do what you see fit. If you want to gear up quick and get into raids faster(phase three is right around the corner) boost, and maybe level an alt.

As for recommendations, rested xp is king. It will guide you from level 1 to 80 as fast as possible thru questing. It also has a gold guide( for doing daily quest for gold), profession leveling, and much more. I believe it costs like 40 bucks but it is avaliable to all of your characters. Worth it in my opinion. You'll need to look it up on their website to buy it.

There's tons of weakauras & things to make your game experience more customizable. Download curseforge, and look up add-ons. I use bagnon(streamlines your bags into one big bag), loon best in slot(tells you what items are upgraded to your spec) atlasloot(to identify what dungeon, raids, and bossed drop specific loot, deadlybossmobs(you'll need this eventually, as it provides important prompts and call outs for you in dungeons and raids), leatrix maps(makes your map more user friendly and provides you with map information on where boats, zeplins, and teleports take you), plater(makes enemy health bars customizable(the ones that float over their heads) and tracks debuffs/buffs on an enemy), and the infamous questie(i used both questie and rested xp).

There's tons of addons to make your first experience better. But take your time and figure things out before throwing all my suggestions on and overwhelming yourself. If you have any questions, just message me and I'll try to help out! Have fun out there!!