Welcome. Your going to have a lot of reading to do
I too was looking at AIO tanks and i finally settled on buying everything seperate. I chose this route because I could get what I wanted for my 28gal. AIO tanks tend to need mods and if anything went wrong with the tank (as happened before to some people) its a pain to get replacements and most people just end up modding to upgrade for better lights, fans, powerheads, etc.
Then again, AIO tanks are pretty much plug and play. Check out the other threads on here and other reef sites to look at both kinds of tanks you want. Whichever turnes you on more, you get.