I am new to the saltwater side of this hobby as well, but I am a couple steps further in my progress than you seem to be keeper, so I thought I could help a little on the sump question.
My set up was designed and purchased through a company who makes custom aquarium set ups, however, my tank is not fully customized as far as being built into the wall or something, but I did have them drill some holes in the bottom of my tank for a sump hook up and some very hidden powerheads.
My understanding is that sumps are very benificial for larger tanks (mine is a 90 gallon bowfront, which is a 72 gallon bowfront, which are more common to see in stores, only mine is taller) and they are much more than just a place to hide equipment. My basic fear was with having kids, I did not want the tank to be anthing near tip-able and so I wanted to put my tank directly against the wall. This cannot really be done without a sump since I would most likely have to hang my skimmer and/or fiters on the back of the tank or at least allow room for pluming to a canister filter. This was a major benifit to me, but it may not be for you.
My second concern was how to keep my water well oxygenated, and at the time I was under the impression that putting airstones in a salt water tank was a bad idea (I have heard some contrary opinions on this lately though). Anyways, my sump also contains a good number of bio-balls on top of which water is casscaded. This helps put air into the water which is important.
I also keep all my mechanicals in my sump (i.e. heaters, skimmers, chiller, water pumps...) and my tank is secured to the wall with no worry about having the need to get to anything I cannot reach. I find them very convient and adaptable so that I can, in the future, create most any type of tank I desire (reef or FOWLR)
You are right though that expense is a big factor in this hobby. I did catch a few breaks that allowed me to afford more than I normally would have been able to, but keep in mind that you can add a sump later on in life. I would stick to what you can afford so that you do not have to skimp on quality equipment just to 'have it all' right away. I would certainly listen to the knowledgable people on sites like this one and do enough research to decide what exactly you need and what will help you have the most success and I am sure you want to have.