(a) 2001-me would drive me crazy, 2003-me would be bearable, but I would love to hang out with 2006-me.
(b) I was sad and scared about failure in both relationships and work in grad school a lot more than I realized. I now think of it as an extremely positive time in my life, but "positive time of growth and learning and so on" isn't anywhere near the same thing as "constantly happy", surprise, surprise.