Newbie questions

I got my first aquarium a few years ago when my roomate moved out and basically abandoned it. It was a 30 gallon tank with an albino Oscar in it. Despite my best efforts, I couldn't keep him alive and happy for more than about a year. He was simply too big for that tank. Since then, I've had several much more successful freshwater aquariums but haven't ventured to the salty side of things yet.
I'd like to get a marine aquarium set up but would like your input before diving in. I plan on getting a 72x18x25 aquarium and setting up the overflows essentially the full 18 inches instead of just in the back corners to provide a much larger perimeter. I've read in several places that a longer perimeter yeilds a smaller cross-section of the overflowing water which is more effective. Is that a good size to start off with? I could go up to a 72x24x24, but would rather the smaller one so that it doesn't take up so much room.
The overflow will drain into a 20 gallon aquarium housing the skimmer, heaters, and two pumps. One pump will return to the display tank via the other overflow, and the other will feed my refugium. The refugium will be a 30 gallon aquarium with about 50 pounds of live rock, some cheato, and an undecided substrate. Is there one that would help keep ph and hardness from fluctuating? Maybe someone here can suggest something that will work well. Oh if I have fish that like copepods, they'll be grown in here, so a substrate that is good for them too may help. The refugium will drain back into the return sump area.
Are skimmers like heaters in that two smaller ones work better than one big one? Or would I be better off just getting one that's slightly oversized? Better to have too much than too little right?
What exactly is a calcium reactor? Do I need one of these things? Are they only useful under certain conditions? These things still seem foreign to me so any help would be appreciated.
I've noticed that sumps typically don't have mechanical filtration. Is that what the clean up crew does, or should I add some kind of filter to my setup? Speaking of cleanup crews, I don't really like snails, so is it possible to avoid them, or are they a must?
I've always liked the idea of alot of plants in the aquarium. Are there some nice marine plants that do well in aquariums and can add some color? I hear they're very good at getting rid of disolved orgaincs and nitrates, so could you have enough of them to eleminate the need for a skimmer? 100% natural filtration is definitely something I'd like to do if it's a possibility.
I've heard that you should use RO/DI water for topoff and water changes. Would it be beneficial to use it for the initial filling and LR curing, or would tap water and a standard tap conditioner work well for that?
I plan on having a few fish and the clean up crew to start off with. If things go well, I'll add some clams, feather dusters, and maybe a few sponges, but not corals. I've heard they're extremely picky about their lighting, and I'd like to avoid things that have strict lighting requirements.

Thanks in advance for the help. Any feedback would be appreciated, posative or negative. I don't want to jump in too fast and kill everything off because I forgot something simple.

 

Although I can't help too much in the beginning of what your asking about the overflow, I think I can help with the rest. I think that snail are a must! They help with the algae and are good part of the clean up crew. As far as plant..... get with reefcleaners, I bought some macro algae from them and I have lots of plant and color all in one. They also absorb much of the nitrates. I bought some mangroves, chaeto and a whole lot of other stuff. I suggest to check them out, they have pretty good prices. And NO 3Reef I DO NOT work for them! LOL '

 

Hiand welcome.

I maybe able to answer some of the questions.

Getting one skimmer appropriate for the tank size and bio-load is ideal. Skimmers and lighting are two things you do not want to skimp on in this hobby. One skimmer should do it.

Most of the filtration is carried out by the live rock, so mechanical filtration is one opition but not the only one. I do not have any mechanical filtration. I only use it when I am cleaning the system.

Snails are important for cleaning off film algae, other algaes, stirring the sand bed and eating detritus. Give them a chance they are pretty cool IMO.

When ever possible use RO/DI or have your tap water checked for phosphates and the TDS value at the local fish store.

Clams are just as hard as corals and maybe more so than some of the simple soft corals. They must have the intense lighting to survive.

Checking with this forum before making any major purchases will save you a lot of money and frustration. Always take the local fish stores advice with a grain of salt and beware of all the items they may want to sell you that you actually do not need.

 

Are skimmers like heaters in that two smaller ones work better than one big one? Or would I be better off just getting one that's slightly oversized? Better to have too much than too little right?
Its better to get one very good one, rated for 2x your tank size
What exactly is a calcium reactor? Do I need one of these things? Are they only useful under certain conditions? These things still seem foreign to me so any help would be appreciated.
no, you don't have corals you don't need one
I've noticed that sumps typically don't have mechanical filtration. Is that what the clean up crew does, or should I add some kind of filter to my setup?some people use filter socks other then that the skimmer will pull out a lot of gunk
Speaking of cleanup crews, I don't really like snails, so is it possible to avoid them, or are they a must?yes, but usually snails work better then crabs, since crabs can't get up glass
I've always liked the idea of alot of plants in the aquarium. Are there some nice marine plants that do well in aquariums and can add some color?
yes checkout reefcleaners.org
I hear they're very good at getting rid of disolved orgaincs and nitrates, so could you have enough of them to eleminate the need for a skimmer?
yes but with a fresh hobbiest the drive to stock is high, so no get one
100% natural filtration is definitely something I'd like to do if it's a possibility.
remember there is nothing natural about raising animals in a glass box, so don't get caught up in the natural
If things go well, I'll add some clams, feather dusters, and maybe a few sponges, but not corals. I've heard they're extremely picky about their lighting, and I'd like to avoid things that have strict lighting requirements.
clams need good lighting like corals, sponges can be difficult at with feedings, plants can be picky to about lighting also(granted less then corals).

personally I think corals are easier because they don't like what algae likes, but to each his own