Here is a list of exemptions.
http://www.state.nj.us/njhighlands/a...exemptions.pdf
Number 5: Improvement to a single family dwelling...
It seems that everything hinges on the amount, % of impervious surface on the property, #2, which states, if I'm reading that correctly, that they don't want you to cover more than 1/4 of the ground. If the house and other buildings, improvements, already takes up more than that, you may be required to add improvements which don't permanently cover, like an above ground pool rather than in ground or a storage shed on piers and not one with concrete floor.
There's not much detail on that page, but it seems that you should be able to do the things you've mentioned.