There's not much to crafting in the game.
Electronics, tools, fabric and gun parts are found in various locations around the map. Once you get close they show up and most will contain 2-3 lootable containers.
Schematics only seem to come from the one off mission rewards so are very limited in how many can be obtained.
They get randomised stats and you won't find a full breadth of weapons as you level and it will potentially take a large number of resources to find a mod with the stat you want. Weapons can be recalibrated but again this involves a cost so will take a long while getting setup.