If you plan on ever marketing your graphics beyond the web (like tshirts and that kind of stuff) I would make sure you ask for any graphics and logos you pay for to be in the highest quality possible. Nothing is worse than building a site, getting popular, and then realizing 'Oh crap this looks horrible on a t-shirt' and wishing you had that first file saved at a higher quality.
Also make sure if you are buying logos that the artist is making them for you in Illustrator and gives you the file in it's original EPS format so if you need to re-scale it down the road you have the best possible way of doing it. Photoshop and Gimp are popular, but they're not really for logos.
Use photoshop @ the end, to build that banner and bring the individual elements together. Just my opinion, hope it helps.