Welcome to you Olive!  I'm not much help, but I'm pretty sure you'll be okay with the pup under 6'.  I don't know of any over that height closed, but will they allow you to open it to service it?
Happy hunting!
Charmaine

Welcome!

I agree that your 6' limitation shouldn't be an issue.  We had a high-wall pop-up a few years back, and it was right around the same height as me (5'10") when closed.  A regular pop-up would be about 6" shorter. 

I don't know what the market is like in NJ, but I imagine you should be able to find something in your price range that will meet your needs.  Look around here and/or Google for some checklists to go through when checking out some units.  Here's a similar thread. Most of the equipment is fairly universal from the most basic popup through higher-end travel trailers, so much of any checklist you find will still apply.  The only things unique to popups are the roof and tent material, and popups tend to have fewer options and more basic appliances (e.g., the water heater, if it even has one, may only run on propane lit by a pilot light, whereas a higher end unit may have DSI (direct spark ignition) and an electric heating element).

One important thing you need to figure out first is what the tow capacity of your tow vehicle is.  Once you determine that, subtract 600-1000lbs (people and cargo in the vehicle) and what's left is your actual tow capacity.  The GVWR (gross vehicular weight rating) of any trailer you look at shouldn't exceed the the tow capacity.  Obviously, there's a little bit of fudge factor there, but that's a good rule of thumb to keep you on the safe side.

Welcome Olive. Glad to have you aboard.