Your goal is to use only Making History parts (or restock+ versions) to get as far as possible.
Level 1: Reach sub-orbit
The DLC is pretty bare-bones, so even this isn't as easy as usual
Level 2:
Standard easy mission, not much to say.
Level 3: Land and return from Mun/Minmus/Poles of Kerbin
Not as easy as you'd think, but challenges faced in orbital capabilities are used here. Lack of jet engines makes this double-level-2.
Level 4: Interplanetary Fly-by and return or Lithobraking
Getting hot, needing excessive tomfoolery and boosters to stretch Dv
Level 5: Interplanetary landing and return
Basically level 4 + level 3 combined. How even?
Extra:
Kerbol/Jool-dive: Try to get as close but still manage to survive.
Multi-mission: Do something like a Mun and Minmus or Jool 3-5. Please don't attempt a Grand Tour for your own sake.
Space station: Your only choice for docking is the airlock and solar panels aren't available.