Thanks everyone. So I finished reading How to Brew and purchased Papazian's book and I'm about halfway through it. The more I read about this and the more I think about costs, I am wondering if brewing 5 gallon batches may be the way to go for me anyway. Here's what i am now thinking though. If I decide to go with a 70 qt rectangular cooler to use as the mash tun, instead of a 10 gallon round cooler, this would give me more space available to brew 10 gallon batches of any gravity of beer, correct? Or, if I want, I can just go with my original design of two 10 gallon coolers, one for mash tun, one for HLT and with that setup, I could brew 10 gallon batches of lower gravity beers, and if I wanted to brew a higher gravity beer, I could use my 10 gallon coolers to brew a 5 gallon batch of higher gravity. Yes, I wouldn't be able to brew a 10 gallon batch of higher gravity, but would at least have the ability to brew 5 gallons of it.
I'm also thinking I am going to need to get a bottling bucket, bottle capper, and other supplies to get me started. Would it make sense to just buy a beginner starter kit that includes the basics for extract brewing since I'll need that stuff anyway? Then, if I get a carboy, I'll have two fermentors for the future and can maybe even try fermenting the same wort in two different fermentors with two different yeasts.