What level is recommended to complete the DLC. I want a challenge, but i remember with FO3 if you completed it when level 30 or something it was too easy. So whats the best level to play it at, that will give you a decent challenge?

For Couriers levels 20+

Yeah I remember point lookout, if you went there to early you got your ass handed to you.

I'm at level 30 and I'd say it's a challenge regardless since at least right off the bat you have no stimpacks, a weapon that takes about 6 shots to kill enemies (my energy weapons and guns are both quite high), melee weapons aren't much better (though my melee skills are admittedly low)... maybe as I progress I'll start thinking it's a breeze, but man... the Ghost people are tough.

I started at level 30 and it's a pretty big challenge, simply because ammo is like gold dust, I swear I've only found about 80 .357 rounds in total, and it takes about five shots to take down one of the enemies.
When I saved I had three crippled limbs, no stimpacks/doctor's bags and no ammo at all.
So yeah, I wouldn't try it with a character below 25 personally.

Level 15 Character here; doing alright. Died once (which is why I'm not playing) but not due to enemies.