get yourself some drt storage whether it be a dry cabinet or dry box... humidity here eats up lenses and equipment...
18-200 is a good wide range lens to start off with... learn to use it properly and if you start to really enjoy photography then consider investing in a little more equipment...
most importantly... have fun its not a competition... well unless you enter one..
The 18-200 is certainly a very versatile lens coz it has a huge zoom range, all in one lens.
BUT.... and I would just like to ask you this:
Will you be using the long end of the zoom much?
My personal experience from shooting landscapes, scenery, etc... is that I much prefer the wide angles. My Nikon D80's 18-135mm kit lens was predominantly used at 18mm, and occasionally from 18 to about 50mm. VERY VERY rarely did I use the longer focal lengths 100mm and above.
Hence I bought a 12-24mm ultra-wide, and it's now my main lens. I'm glad I didn't buy the 18-200 coz it would've been a waste for my preferred type of photography.
Important thing is to find the focal range that you'll most likely use, then get the lens to match it.
Don't buy a particular lens just based on others' recommendations.