You'll find a lot more variety in kit recipes if you stick to 5gal size. Just cut it in half and you've got yourself two 2.5 gal batches. Use the same kettle, just get a bag from wilserbrewer. Plus you can get 3 gal fermenters cheap, either glass or plastic. ($20 for plastic iirc)
that way you can order kits from any home brew supply, not just northern or Midwest. WAY more selection and variety.
Plus it lets you be more creative. Stout kit- half normal, half milk stout, coffee, etc. try their ipa kit, then use your own new favorite hop in the other half. Take a wheat beer and do half Hefeweizen, and half sour Berliner style.
You'll want your grains unmilled, so you should get a cheap mill to use. if they are shipped in separate bags for each grain, just use half. If not, then make sure you thoroughly mix up the grains so that your proportions are the same for each half. If you don't want to get a mill, then just make sure you mix them well before splitting, and either use the second half soon or keep in sealed tight.