The bigger the pot, the better. If you're looking to do 5 gallon batches as most of us do, a 7 gallon pot is ideal. A 6 gallon pot will also work, but you'll have to either keep a close eye on it to avoid boilovers, use slightly less water, or invest in anti-foam agents. Basically, the more of your batch you can boil, the better your hop utilization is going to be. Because of that, your beer will be improved greatly. I started off with a much smaller kettle than that, and my beer was fine. Use what you're comfortable with, and what you can afford.
As for the starter kits, I think Midwest has the best deal in town. $110 gets you their Intermediate starter kit
(linked here) which has 1 primary fermenter, and two 5 gallon better bottles. You probably don't want to use the 5 gallon containers for primaries (although I have for a couple of batches, I just had to use a blowoff tube) but you can if you want. Either that, or use the fermenter bucket for your primary, and as soon as you rack to secondary, you can pitch another batch into the bucket.
I'll also recommend a few additional items that you may want. A jet bottle/carboy washer is cheap, and will help so much. Just be sure to also buy the faucet adapter so you can use it on your sink. An immersion chiller is also a sound investment, and they sell a stainless steel one for about $50.