Welcome, welcome, welcome.
That is a lot of questions, and unfortunately, none of them have definite answers. I will give it a shot, but others may have some more to say. A couple things to think about are what type of setup you want. do you want a reef tank, fish only, fish only with live rock? these decisions impcat greatly on the answers to your questions.
As far as difficulty is concerned. Its not. flat out, this is not a difficult hobby, it can be challenging, but I am going to guess that most peoples frustrations result from one of two lacking things. Lack of knowledge, or lack of patience. This is a hobby that requires as much of these as you can muster. So this is not a difficult hobby by any means.
Maintenance also depends on the type of set up you have. It simply requires routine. For example my tank, there is minimal maintenance involved. I add freshwater every night, feed, every other day, and change water once a week. thats it. Others have systems that are far more simplified, but others have some that are far more complex. The maintenance really depends on how you set it up.
I hope this helps a little, and with a little help from you we can get your tank up and running in no time.
this is the best advice i can offer you. right here, this is it.
READ AS MUCH AS YOU CAN, LEARN AS MUCH AS YOU CAN, BEFORE EVEN PUTTING WATER IN.
I waited six months, and all i did was read this board. I promise you 100% that i saved myself hundreds of dollars, and hundreds of headaches. you dont have to wait that long, but i would wait a little bit at least.