All wood reacts to humidity so during the summer months wood is likely to expand in the humidity of the warmer, wetter months and contract in the cooler, drier winter months. Installing a humidifier to maintain the humidity levels in your home will help reduce the gaps you see in the floor. Engineered flooring does not expand and contract the way a solid wood floor does so it reduces the the chance for gapping.
Anything you can clean your windows with you can clean your floor with. Spray a little cleaner on a soft terry mop and wipe down the wood. Make sure that the floor is first clean from any debris or dust by using a soft vacuum head before going over it with cleaner. Do not use any polish or wax on your floors.
Yes. Exotic woods will change colors. It will take a few weeks to a few months for it to deepen in color. Check with the flooring company to see if the floor species you have chosen will change color. Some domestic woods will also change color going either darker or lighter depending on the wood.
Place area rugs over high traffic areas and put felt under furniture and chairs. Place a rug outside that traps debris in the shoes before it comes into the home.