I don't think at all that is overkill, it is a fantastic lens. The one thing that concerns me is that you might find it a little long on a 1.6 crop body if you are interested in shooting a lot of landscapes. On a 1.6 crop body, the effective focal length of the 28-135 becomes 44-216mm, which becomes a fantastic portraiture length and telephoto, but is not going to be super wide. If you have a chance to test it out or rent it first, I might do that. If you find that it is a bit to long, you might look at the EF 17-40mm f/4.0L, a bit more expensive, but a killer lens, especially for landscape work. You should probably go down to a camera store with a compact flash card, and ask them to shoot a couple of frames with the lenses you are interested in, then take the card home at look at the image. Who knows, the 18-55 might be exactly what you are looking for (the IS version is pretty different than the kit lens version, very oddly and confusingly there are like 5 different versions of this lens). There is also a handy site over at
the-digital-picure which you can directly compare two lenses (select the two you want then roll over the image to compare)
You are probably going to want right of the bat extra batteries (which you can get cheap but good knock offs from places like
SterlingTek), memory cards, tripod, a bag to carry it all in. Then you need to think about how you are going to process your images. If you are shooting low volume, the software that comes with the camera isn't bad, but if you plan on shooting a lot, you might need to look into something like Lightroom by Adobe. That also means that you are going to need a computer which has storage space, so that might mean an extra hard drive (or two to have one to back up on). If you want to get into heavy photo editing, you might need then to look at something like Photoshop.