Yup. I agree that a flat tarp will be a fine first try. It is really hard to get it wrong. The flat seams also allow you to add a third fold. This adds strength much like a wire framed mock-up. This lets you do away with internal supports and reinforcements. For example, used only on the four corner seams, it adds quite a bit of strength for minimal weight at the cardinal, or primary, guy-out points relieving stress from the fabric. You end up with a more durable tarp.
Refer to http://en.wikipedia.org/wiki/Tensile_structure for information on cat curves. Likely more than you wanted to know. Basically, you can approximate the curve with a large single radius. Usually, a 1" in 72" is enough. Most manufacturors way overdo it.
Attaching guy-outs is basically just adding a small reinforcement patch for cardinal points. It really depends on your staking stress. A LOT will depend on whether you want a solid anchor, one that flexes a bit, or, a loose anchor. Almost all UL tents use a loose anchor. The stakes will usually pull loose before the tarp will shred itself. This can vary a lot depending on soils, rocks, etc, though. A typical tarp, staked every 3 feet with a shepherds hook in moderate soils will withstand about 35-40mph. LONGER guylines can improve staking power. Tying off to trees is an example of a solid anchor. Something will be destroyed before it will come loose. Tying off to a low hanging branch is an example of a flexible anchor.
I use UL strapping, often with reflective coloring about 8"-10" long. Leaving just an inch hanging out, this has been more than adequate. I then tie a short loop of bungie or shock cord(doubled hair-tie) that I stake to. This helps to relieve wind hammer on the stakes, provides some cushion for gusts, and, supplies some take-up for soaked fabric…usually silnylon. I was using elastic strap, but this wore out after a few years.