How should internal links be handled for example links to TOS and other pages not needed in search engine results. Should I use the nofollow tag? or could that be detrimental to my serps?
Just link to them normally. No need to do anything fancy with them. Most websites have these types of pages, so Google know how to treat them. They certainly won't penalize you for just linking them as any person with limited HTML knowledge would do.
No follow is useless now for PR sculpting, but it is still good for tos and pricacy poilcy pages, contact forms and things like that. You can always do some link consolidation and take all the TOS type pages u have and put them into one page, then just use anchors and anchor links to navigate (example: http://www.rehabilitation-center.org/addiction-training-seminars.html) Hope that helps. You can also go down the iframe road or javascript links, but I find that to be a pain in tthe @$$
I would just put tos and other things you do not need links to on one page. Then link to it only on pages you need to.
yes, I would no follow all the unimportant pages, because then the links juice will go to the important pages, I would no follow things like contact us, privacy policy, login, register, tos etc
I don't think the no follow tag would really be worth the time. Unless lots of people start linking to your TOS page for some strange reason, I can't see why an internal link would make enough difference to hurt you.
Interlinking internal pages is good and it is better if you have relevant contents. So, try to install some plugins that do it automatically. Regarding nofollow tag, no don't use it here. It is best to be crawled and it will give some credit in your SERP ranking too.