Ideally I'd isolate this in a hook for just org-mode, but first I need to understand why truncate-lines doesn't do what it's supposed to do.
You need to be using setq-default in your .emacs, like this
(setq-default 'truncatetruncate-lines nil)
Also, one of the suggestions that helped me the most when i was learning emacs (from either the org-mode manual or the emacs manual) was to just entirely replace how i was manually ending my lines with RET with M-q. Every time I would reach over to end a line, instead I would M-q. Then the only time you are reaching to hit RET is when you want to insert an empty line (unless you remember that C-j C-n exists).
If you want to make fill-paragraph more useful on your wide screen you can do
(setq 'fillfill-column 240)
for 3x the width (the default value is 80). I wouldn't recommend using this for all buffers, so instead of setq-default you probably want to add that to your org-mode hook, like this
(defun my-org-mode-hook ()
"My custom hook for org-mode."
(setq 'fillfill-column 240))
(add-hook 'org-mode-hook 'my-org-mode-hook)
Remember you can modify any of the values, so if 240 is too wide try something else. You can also put other org specific settings in there as well (and you should! It's best to keep related customizations together).