1.Stats: Should Golurk get a stat boost, Evolution, Mega Evolution or nothing?
Golurk is a weird species, which started off as a late-game species in Unova and reduced to a mid-game species in Kalos. This was largely due to its base stage, Golett, being 303 BST and evolving very late, around Level 43. While this might mean Golurk should have a large BST, the reality is that Golurk already has a 180 BST gap, which is one of the largest gaps in the game.
This means a stat boost it can theoretically get can only be around 10 to 20 BST, which is insufficient.
An evolution is also infeasible, as Golurk is gigantic.
This leaves Mega Evolution, which will not be usable without a stat boost first.
What Golurk really needs is buffing its base form, or gaining a middle stage and then a 50 BST upgrade. Anything else seems insufficient.
2.Should Golurk get more abilities?
Golurk has decent abilities, though only No Guard is any sort of relevant. Outside of that Clear Body, Contrary, Illuminate and Wonder Skin sound fitting.
3.Should Golurk get more moves?
Yes. Golurk's movepool is okay but it can be improved significantly. Most obvious update would be Shadow Sneak, Trick Room and Bulk Up, but other moves like Meteor Mash, Mach Punch, Focus Energy, Wide Guard and Iron Head/Head Smash can be granted.
4.What additional typing Golurk can have?
Fighting is the most obvious one, and Steel and Psychic are lesser options. Rock and Normal would be the least options.