80-120 is about right. Re: the last sentence, some guys - on reputation - just "get" a pick...Hakan Andersson is a good example in Detroit.
Not all teams do it the same way, of course. So you could reasonably conclude that on your list of 120, that maybe 13 of the bottom 15 won't get drafted at all for instance...so if you wanted to cut it up (for purposes of making it digestible for the media) and say, "ok, our 1-18 are probably the first rounders...our 19-53 probably round out the rest of the top 100...our 54-80 are probably the rest of the mid-rounds...and then our 81-104 is probably 6, 7 and beyond..." or whatever...
Because not only are you doing your own research, but you're also talking to other people in the game...you have friends in the industry, just like any other...you bounce ideas off of, you gain knowledge, their perspective, etc.