>>1316358Knives you need:
Primary belt knife (3-4 inch blade)
Small fixed blade (2-3 inch blade, usually a neck knife, mostly for opening packages, dealing with fruit, etc.)
Folding knife - either a classic slipjoint, or a modern folder
specialty knives - all the oddballs with a narrow application
multitool - either SAK, or leatherman
That will cover all the bases you need, without stepping into "collector" territory.
As for collecting - either look for knives that are somehow significant (buck 110, delica/endura, F-S, etc.), unusual designs (yakut, canadian belt knife, etc.).
Pic related is some of mine. I generally try not to buy six of the same type of knife.
Of course, I only use a fraction of that - mainly 2 or 3 belt knives, and a few of the smaller fixies + a couple of folders (depending on what I feel like carrying on a particular day).