stanleo said:
3. Don't rush anything about it. Take your time, do your research and research every individual animal (individual corals included) that you want and have a plan for what you want the end result to be. 4. Listen to Donya, she knows her stuff!
This, to me, is the biggest difference you'll encounter. The closest freshwater tank to a marine system is a high tech planted tank, but the fundamental difference between the two from the care point of view is that high tech planteds give rapid results (like stems hitting the top of the tank in 2 weeks) and the care requirements of the stock tend to be fairly similar. Marine tanks, in contrast, move very slowly, and different critters can need very different environments or tank positions. Although both require the intense maintenance.
Otherwise, yes, listen to the advice that's on offer, the nice thing about slow and steady is that it gives you lots of time to share ideas here. Marine journals tend to end up long, and fascinating, reads, and, as you read, you'll see that things never seem to work out the way people intended, which is half the fun.
As for your tank, you'll struggle to get a sensible sump into the stand of a juwel trigon, but otherwise they make good marine tanks, the shape lends itself well to live rock structures and it's relatively easy to get a good sense of depth in them. I've seen one with a nice refugium/sump placed to the side of the tank (it was actually a through the wall trick, as the tank backed onto a cupboard through a partition wall, which was great as it kept a lot of noisy kit out of the TV room).