I know the answer, but the character isn't really threatened so far?
Of course he is! It's very very difficult, and if I mess up too bad, he's dead, but it's doable, on Master. On Adept, it's a perfectly viable playstyle, and on Novice, you can get away with some more skills, like Alteration, OR Restoration. The point is to limit your level so Destruction is still a viable damage dealer. I'm also Power Leveling him, because he has to do twice as much damage, and therefore gets twice as much XP per fight. The enemies tend to live long enough to get at least a shot in, so I have to Block, and take some to the Armor, but not too often to survive. That is a Master playstyle though, not in terms of game difficulty, but how much you, the player have to know what you're doing. For a novice player, it's a real good trainer for Blocking, and Magicka Management. You don't just run the blue gauge down, because you also have to maneuver, and Block, and you're light enough for Stamina to hold out, but it really helps to know where the easier fights are, and avoid the really dangerous ones.
So, let me see if I understand this correctly. If my sidekick kills the draugr, does she get the experience? As in, do the sidekicks level up, do they just match my level, or is their level preset to when I meet them?
No. First, you don't get Experience except for the damage you do yourself. Even indirect damage from the Burning effect of Flames, either Bleeding effect, or spells that can turn the enemy against each other don't count. Other skills gain experience in other ways, but the general rule is you get XP in a given skill by using it successfully with a valid Target. If you shoot at one of those straw targets with a bow, no XP. Any NPC (Everyone else in the world) will give you experience for shooting them proportionate to the Damage. Even your follower if accidentally. (Don't make a habit of it.)
Followers are supposed to level with you, but generally don't. I save the really really good ones (Belrand, Jenassa, and Eola for my short lit) Until after at least 25 so I get them at their best. Also, they tend to kill too much at lower levels. The best follower for any given character depends on that character, and the player.
Erik the Slayer, because he's Light Armor, and can sneak, but also uses 2H weapons. You just got the Skyforge Steel Greatsword (SFSGS) so it's better than just selling it. As an Archer, you will usually want someone forward so you don't have to spend so much time running around instead of Shooting. With your Shield out, you'll want to get a bunch of hits in, while still having some Help, so you don't get overwhelmed. Erik can be powerful, but still swings slow, so you can get your hits in too, he's not just going to Pwn every fight, and keep you from leveling your combat skills. (He's also one of the few with Light Armor, and 2H in combination.)