From what I hear, salt water aquariums are MUCH more labor intensive than fresh, so it really depends on how high maintenance you want it to be. Also, if you decide to go with a salt setup, make sure you get a tank that is not too deep, you want to have a lot of surface area so that the light can get to your live rock or it will not survive. I think you can have much more color in a salt tank, fish tend to be brighter colors and lots of different types/sizes can live together depending on your set up.
I have a 125 G fresh and a 30 G fresh. You can set up community tanks with several different species of fish or set up with several of the same species. I personally have aggressive tanks and my fish would typically not do well in a tank together, however, my hubby is GREAT with fish and makes it work. I have two Pacu's that are about 20" long, a Flower Horn Cichlid that is about 5-6", a Red Devil Cichlid that is 4-5" and a Male Blue Johanni Cichlid that is 3-4" all in my 125 G. Both the Flower Horn and Blue Johanni had been sold and returned to my LFS because they were too aggressive, but we have had them living together for over a year and they are fine. I also have two Pleco's in that tank. The 30 G has four female juvi Blue Johanni's, a Dinosaur Bashir and a Striped Raphael Catfish (which we NEVER see). Once the females are large/old enough, we will move the male in with them. Whenever we are adding new fish to our aquariums, we always start by repositioning the tank decorations which means all the fish are re-establishing their "territory" and no one has time to worry about establishing pecking order. This prevents the established fish from pestering the new fish to death.
When starting a brand new tank, get your tank up and running for a full week prior to getting fish to get your temps established, then add throw-away fish, feeders are good cause they are cheap. These throw away fish will help to establish your bio-filter and a tank with no established bio-filter will not keep fish alive for long. Another option is if you know someone that has a well established tank, ask for their water the next time they do a partial change, a couple gallons from an established tank will also jump start your bio-filter.
We have two Magnum 350 Canister Filters on our 125 G and I love them. We also have a bio-wheel, which also helps with that bio-filtration (good bacteria). I would not recommend going to any of the big chains for advice on setting up your tank or buying fish (generally speaking). Go to a few local small fish stores and check out their tanks and fish. Pay attention to how the store smells especially, it should smell clean, not musty or mildewy, the tanks should be clean and the fish should appear lively and healthy. Fins that are held close to the body is a sign of stress or illness, the fish should be free of external parasites as well. Also, ask what days they get fish shipments and make sure you check out their stock in between fish delivery days. Fish delivered today may be stressed from the move (normal), but may also be healthier than their normal stock if they are not caring correctly for their tanks. You can certainly buy equipment from chain stores and may be able to get a better price, but the live animals are typically healthier in small, non-chain stores. Read up on a few things, then go ask questions you already have answers to to help determine if they are knowledgable.
I would love to share pics, but do not currently have any pics hosted online. I'll get some up in the next couple of weeks, though. We have plans to eventually build a 400+/- G tank in the basement to house the Pacu's because they WILL get BIG. Make sure you research the fish you want before you buy. There is a type of fish that I would LOVE to have, but it requires brackish water which I do not have, so I am unable to provide an enviroment it can thrive in, so it remains on the wish list. I did however find a freshwater fish that has a similar look, so bought one of those instead. The Pacu's are another perfect example of why you should research. We bought them at Walmart when they were 1/2 Dollar sized with no prior research. We knew they got big, but did not know they could reach 3' long. I really love these fish, lots of personality and just really cool, so we now have to plan a way to house them because they are our responsibility and we plan to keep them until they die of natural causes (30-40 years from now).
As far as moving, it depends on the size of the fish and how far they are moving. When we moved our tank from place in the Living Room to another, we had to put the fish in Sterlite type containers with water from the tank, however, if we were moving to another house, they would also need at least an aerator and possibly heat depending on ambient temps. If you have just little fish, you can use a clean five gallon bucket for all the fish, just secure the lid and get a battery powered aerator until your tank is set back up (moving a tank with water in it is NOT going to work).
Also, I hear that larger tanks are actually easier than smaller tanks, so try to go 20 G or larger, anything smaller becomes more difficult rather than less.
Sorry this became so long, I really enjoy my tanks and they require very little care at this point so I can just enjoy them without lots of work. Take care and good luck getting a tank (or two) established.