Very well done. I hear you on the feeling like you don't know what you are doing. A few questions:
1) Did you look up plans for building a table so you knew how to put in those corner braces, or did you just look at other tables?
I did some research about different ways to build tables, but mostly just looked at pictures. This one is a combination of 4 or 5 different table designs that I looked at.
2) How are you going to add an extension when the boards on the table top go the long way?
I have some left over boards. Basically they will be like the breadboards, with 2 2x2s screwed into the bottom. The 2x2s will slide into the channels. Here's a pic of somebody else's to help explain:
http://tommyandellie.com/wp-content/...-Revised64.jpg
3) Has it cost you 3x what you thought it would yet?
Yes, at least 3x. I didn't keep track of how much I've spent. The single most expensive part was the power planer. I bought it off craigslist. I would have just taken the boards somewhere, but nobody wanted to run old boards that could contain nails, screws, dirt, etc. through their machines. I'd say that in total, I spent around $400.
4) Have you gone on a shopping spree buying tools that you've never even heard of before, but are now sure that you NEED?
Just the self-centering doweling jig. Everything else I either had already or had heard of before/knew I would need.