Don't even THINK about a salt water tank!!
I have had a salt water live reef tank for MANY years then finally shut it down. This is not something you just sit back and enjoy especially if you travel. Mine was a 65 gallon tank with all kinds of beautiful fish, invertebrates and high-tech hardware. The water MUST be very, very good and maintained at a narrow range of parameters. It requires almost daily maintenance otherwise the contents will definitely suffer. We have very high quality drinking water, but that water is not acceptable in a reef tank without pre-treatment. How's the water where you live??
I used a series of activated carbon canisters and reverse osmosis filtration system to prepare the water additions to the tank. Even then, you can't just add cold water to the tank, it has to be preheated. Moreover, the salinity and pH has to be adjusted and allowed to equilibrate before adding water to the tank. Think about how and where you would store this water.
What about power outages? You have to keep the tank at about 80 F so the heaters and lights need to continue to operate. Then again, what about hot summer days? If you don't have appropriate air conditioning, how will you keep the water in the correct temperature range? Lighting is designed for the tank so you have to use special bulbs and those contribute heat to the system.
The tank also has an internal system of filters and biological treatment to continuously clean the water. Those filters must be changed almost every other day. Think about who will perform that maintenance while you are away from your home.
Needless to say, tropical fish are expensive and so is the equipment. The price of a 40 lb container of marine salt is also spendy.
Also, be aware that not all fish will get along. It's sad to introduce a really nice, expensive new fish to the tank then see it immediately eaten by one of the occupants!