Yes - welcome to my extremely busy Harry Dresden board!
To answer your questions:
1st - noooooooooo no death to Codex Alera! Why? B/c it really isn't taking away from Jim writing the Dresden series. See, his contract is to release one Dresden book per year. So, we have to wait until next August for Book 6, which, IIRC, he's already written. He may be working on book 7 even. So, you'll just have to keep a look out every August or so for the new ones. Ugh! If there are gonna be 20 books and we're on 5, that's 15 more years! Eeep!
2nd - I've heard, straight from the horse's mouth - so to speak, it was via email - that YES, the Dresden series is planned to be around 20 books long with a trilogy capstone to the series. Now, will this become a reality? Hell, yes, if I have anything to say about it!

(yeah, like *I* make the world go 'round) --
In the meantime, you can grab the audiobooks for the 1st two books of the series -- "Storm Front" and "Fool Moon" -- both read by the amazingly talented James Marsters... and available here:
www.buzzymultimedia.com
And yes, I must tout the talent of Mr. Marsters for these books b/c, if not for him, I wouldn't know anything about them. (And I run a James Marsters website, wouldn't do for me to not promote him in some form everywhere I go

)
Again - welcome and have fun posting!!
Highlander II
James Marsters.info
Highlander II's Medium-sized Kingdom
Harry Dresden - wizard
"Yeah, I could do that, but I'm paralyzed with not caring very much." -- Spike