Let's see.......first.....try and picture your tank with 45-70 lbs of live rock in it. How much room will your fish have to swim in? Along with that, since the majority of your internal tank volume will be consumed with rock, how many fish do you think you'll be able to put in it? second..........with all that
LR in it and all the nitrification going on, what do you think the chances will be that you'll be free of hair and other algae growing wild because you don't have a skimmer or some other kind of mechanical filtration to remove waste and export nutrients that WILL be given off by the rock including the ever loving nutrient PHOSPHATE?..............and you'll need massive circulation to keep the detritus in suspension so it can be captured by some kind of filter to get rid of it because it won't be able to break down fast enough............so with sand you'll and all the circulation you'll need you'll have massive sand storms..........
CC will not give you that problem because it has weight to it. Don't let anybody fool you......sand collects and retains detritus also. Your tank will look like a rocky mountain snowstorm if you have the proper circulation. Third.....refugium.....why? Your
LFS guy is right...........for his suggestion of faux rock at least, because you won't have the nutrient problem therefore you wouldn't need a vehicle for nutrient export. With
LR in the tank, the skimmer will do that for you and as far as the bak/pak combo.........not a bad choice.........you'll get nutrient export and mechanical filtration.
Your
LFS guy trying to KISS it for you.
Your local guy isn't far off track..........he just didn't explain it very well to you