On my first playthrough I didn't collect all artifacts and unpgrades and I'm now on my second. As long as I don't fire at the final boss in the centre at the end, initiating the battle, can I go anywhere on the map as much as I please? I noticed I'll have to do some backtracking to get some collectibles.
Also, I'm up for getting the two lantern run cheevos online. Add me if you need a fourth.