First off I'll state that I'm not a collector. I carry and use my knives. If they end up not getting carried and used at least periodically, then they end up being sold or given away.
Personally I set myself a limit on pocket knives (or anything else I might become prone to excess with). This is based on what fits my budget and most importantly is just based on practicality - how many knives can you carry (OK I know everyone will have their own answer to this, from "one" to numerous, but most of us would probably say one or two, some may say three)? The knives I buy are based on my taste and preference according to type of use, etc. In my case I prefer the old fashioned traditional slip-joint pocket knives. I generally carry two - a small one and one of medium size. The total number of pocket knives I have is set at a personal limit of about a dozen (+/-). In my case (not being or desiring to be a collector) I just can't see much sense in having dozens or hundreds of knives. I carry and use them (some more frequently than others). They all get pocket time or I end up gifting them or selling them off as I personally just don't want or need 100 knives. To me a knife is a finely crafted tool that deserves to be carried, used and maintained like any other fine tool deserves. To me, sitting in a safe or drawer is just not the fate a fine knife deserves. Carry it! But if you have 100 knives for example, how much time can they really see use? Realistically it's very little if trying to juggle so many through a carry rotation. I keep it simple and keep it to a small number of very choice favorites. If I come across a knife I "just can't live without" then something gets sold or gifted generally.
Some day I may even drop that number to around 5'ish but for now I have around a dozen and enjoy them very much.