What to do with all my weapons ?

My inventory is full of all kind of weapon, should I upgrade them to 5 stars and extract them ? I read on this sub that I should finish the collection of the kind of weapon I want to extract before doing it, but I thought if you get the weapon once it still stays in your collection even if you sell/extract it ? Also there is no way I can do all the collections with my inventory being already full and I'm nowhere close to finishing any collection

What am I missing ?