+1 on the bigger isn't always better scenerio.
You want to start big enough that water parameters can't turn in an instant (my 5 gallon planted pico tank is harder to maintain than my 90 gallon reef), but not so big that costs and the time to maintain it are a huge step.
I would reccomend a tank in the 40-75 gallon range. Big enough to keep water parameters stable, small enough to afford. Stick with a standard shape, as bowfronts, corner and column tanks can have unusual flow, lighting and maintanence needs that a beginner doesn't need to worry about.
If you can, the 40 gallon breeder and standard 75 gallon tanks are a wide, shallow shape that makes reef lighting and aquascaping much easier.
Also, try to go with a reef ready tank, if at all possible. My first tank wasn't reef ready, and I spent more buying, replacing and again replacing filters and HOB overflows to get my filtration right than if I'd just went reef ready with the sump from the start.
Used systems can be your friend. A lot of private LFS sell used systems for cheap, and you can find them all over online.