If you are going to do a partial boil (boil around 3 gallons, then add in tap water to make it 5), a 4-5 gallon pot will be plenty big enough and will be easier to store. You won't need a wort chiller because you can put the extra tap water in the fridge (inside your sanitized and sealed bucket/carboy) the night before and have 70 degree wort within 69 seconds of finishing the boil. But many brewers prefer to do full boils once they get the hang of it. It requires a bigger pot and a wort chiller, but you will end up with better beer.
As schokie said, you're going to get out of the hobby what you invest in it. If you only want to spend $69 on a Mr Beer kit, you're going to have homebrew, but it won't be nearly as good as beer you could make if you invested the time and money. Ignoring the equipment costs, my beer costs me less per pint than a comparable beer would at the store, but including the equipment makes it much more expensive. But there is some satisfaction knowing that I haven't bought a beer at the store (except for roll calls) since I started brewing.