I haven't had to care about how many Cores or Shards I use for a very long time, so take this with a pinch of salt, but I don't think that weapon crafting is meant for new players. Aside from the quests that introduce you to how crafting works, a new player is very rarely going to come across weapons with obtainable Patterns. By the time they are able to craft a gun, they'll likely have developed their own preferences for archetypes and perks, at which point they're educated enough to know which guns they want to craft and which ones they don't. Excluding weapons that I've crafted solely for Triumphs and Challenges, I've only crafted 13 Legendary weapons and 4 Exotics in the year-and-a-bit that the system has been available.