I’ve been using 2D concepts of weaponry, like this:
And i’m planning to clean them a little bit, make just the overall shape in black, and import them into blender and extrude it. This way, i can have a really good base for high-poly detailing, specially through kit bashing. Do you guys know any way of doing this? Also, do you recommend this kind of workflow?
I just find a pain in the ass to connect little dots in order to blockout my stuff. 
I do not know if I understood the meaning of the question? . . . but you can use your image in the background.
==> Hit N-Key to display the panel et go to [Background images]
You can also use a plane for display your image:
==> File > Import > Images As planes (the Addon must be activated) . . . :o
I believe the meaning of question is how to draw 2D shape and extrude it afterwards.
He basically wants to extrude the silhouette of the guns.
@OP
You’re going about the wrong way of modeling weapons.Model the weapon parts as separate meshes,also don’t play “connect the dots” as it’s horribly inefficient.
First start by modeling any circular bits like the barrel since they are the easiest to do from a 2d perspective.The rest of the gun can be modeled by starting with a plane or cube and then extruding it to shape the different parts,make necessary loop cuts,scale and pull vertices to define the form of the part.After that you can use the knife tool to add details where they are needed,remember to keep proper topology and edge flow if you’re going to be using the subdivision modifier or if you’re going to texture the object.
Repeat the step for the other parts of the gun.
