You'll want to use the 18-55mm. The 55-250mm is meant for things that are further away than you're likely to place your clothing.

The 17-55mm f/2.8 can work in lower light (doesn't matter for non-moving clothess, lit with a flash). It can also create a thinner depth of field (or DOF). This is just a measure of how much is in focus, and how quickly background or foreground elements go out of focus. If you place your clothing items on a surface, both lenses will work the same. If you place your clothing on some sort of stand, and put something behind to act as a background (fabric, poster board, whatever), both lenses will be act identically. If you place your clothing items on a model, with a solid background, both lenses will act identically. If you place clothing on a model, and you can't control the background, and want the background blurred, the 17-55mm is the better choice. I'm expecting the 18-55mm will be just fine.

If you're shooting lots of images at once, consider Lightroom. If you're shooting a few images at a time, Elements works fine. I use elements 10. You can also use the DPP (Canon Digital Photo Professional) software that came with the camera. It does everything you need.

Until you get your lighting kit, I'd suggest using the following settings:
Mode dial M (manual mode... except you're going to tell the camera to figure out ISO)
Set the Aperture (Av) to f/8.
Set the Shutter Speed (Tv) to 1/50s. Should be fast enough to hand hold without blur if hold the camera steady when pressing the shutter button.
Set the ISO to AUTO. ISO is like a volume control for light, and we're telling the camera to figure it out for us.

By setting a fairly slow shutter speed, you can work in dim indoor light. But setting a fairly high aperture value, you ensure you have everything in focus. It's also slightly above your lens' widest aperture (f/5.6 at the 55mm end), which helps sharpness. Many lenses don't perform their best wide open.

If your ISO goes very high, your images will have a lot of noise. To combat this, you'll need either a tripod, so you can lower your shutter speed, or your flash kit, so you can add more light, or just move yourself to a brighter location (but not direct sunlight! Shaded near bright sunlight is great).