[I’ve never really messed with redirects before, but here is the situation. I have an old domain that is a PR4 and it is not being used by me anymore because I got a new exact-match domain in the same niche. Now please correct me if I’m wrong, but if I do a 301 (permanent) or even a 302 (temporary) redirect pointing that old domain to my new one, that will flow all of the link juice to the new site, correct? Then the new site will be a PR4 as well?]
A 301 Permanent Redirect passes link juice, and a 302 Temporary redirect does not.
There is a decay factor built into the PageRank algorithm that will reduce the strength of your current PR by approximately 15% so you will need to do some promotional work to make up the difference, but most of your link juice will transfer through a proper 301 Redirect.
If you 301 to your new domain you have redirected all of your link juice to the pages of that new domain. Google doesn’t assign PR to domains it is applied at the specific URL and it is internally updated with each new query.