[asylumdown]

I'd say the answer to all your questions is 'depends on what you want to keep'

Are you converting your cichlid tank, or starting over new? If you're starting over new, why do you want to use a canister filter? The only reason I'd use a canister filter on a new set-up would be if I already owned it and I was trying to contain costs. Mechanical filtration on a reef set-up is much more efficiently achieved with either a sump with filter socks, or some sort of an overflow that flows over easily removable foam or mesh as you are far more likely to change those out or rinse them every couple of days. However, I would argue mechanical filtration in the sense you're talking about aren't really needed in a reef tank, and there are thousands (millions maybe) of people who run beautiful tanks without it. Reef tanks develop a much more complex food chain compared to freshwater tank, with hundreds to thousands of small commensal animals, both sessile and motile that process left over food/fish poop. Also, canister filters are designed to do one thing, and they do it very efficiently, and that's convert organic solids in to nitrates. It sounds counter-intuitive, but one of the secrets of a well set up reef tank is preventing as much bacterial nitrification as possible, or at least preventing it from happening in places where there's no chance for it to be further anaerobically reduced to nitrogen gas (which is more likely to occur when the nitrate is produced in the top few mm or live-rock as the nitrate vs diffuse in to the rock from the water column)

Also, the rules of pound per gallon of live rock are all over the place because I'd say there really isn't a true 'rule' anymore. The answer for how much you need is as much as necessary to keep ammonia/nitrite levels in your water undetectable for your fish load. I think it's been demonstrated over the last 5 years that the actual amount is a) WAY less than what people used to believe in the 90s and b) variable depending on what else is in the tank and the quality of the rock. Nitrification happens on all substrates, so if you've got sand, it's going to be helping out too.

Minimalist aquascapes have been all the rage the past few years and I've seen some jaw dropping reefs with what can't be any more than .25 pounds of rock per gallon of total system volume. I have yet to see a single thread anywhere of someone saying "my ammonia levels just won't come down" at X amount of rock per gallon, so I'd say you need as much rock as you require to build the aquascape that looks good to you.

anyway I could ramble on and on... but welcome to reefing!

Oh ETA: I would go with mostly dry rock like Fiji rock if I was starting over, but that's just me personally. The kinds of living things that you can't pay for that show up eventually that are good (pods, certain worms, sponges, coralline algae etc.) are next to impossible to keep out even if you wanted to. What you do want to try your best to keep out are some species that are universally regarded as pests and can ruin your enjoyment of the hobby. I'd give 100 bucks to the first person who could find a LFS live rock holding bin that didn't have at least 2 different pest species present.