TK - if your set on keeping your Expy EL, I would agree your trailer weight MAX, IE the trailer's GVWR should be NO MORE than 7K. Honestly if you think you really will have 1200# of gear/people/supplies in the expy in addition to the trailer TW, I would really try to stay in the mid 6's for trailer GVWR and DO NOT listen to any salesmen who will try to tell you "ooohhhhhhh you'll be FINE, that Expidition of yours will handle it no problem." more often than not, it's total BS and they just want to sell you a trailer.
As an example, I have a 7 yr older Expy than you do and mine is the standard length Expy, not the EL like yours is (the longer wheelbase of the EL is better for towing). My 89 Layton has a 6K GVWR and the title says it's 3500 *unladen* which I think is low. My trailer is 23' ball to bumper. Fully loaded up and ready to camp I think I'm probably north of 4500, closer to 5K.
The 5.4 in your 07 I'm sure has more HP and torque than what my 00' has, however with me, my wife, both boys, gear in the Expy, I bet with the firewood and other things I had probably easy 500 lbs just in gear alone, plus us, so probably another 550 lbs for us, so 1K total in the expy, gear and occupants.
At any rate, it felt HEAVY to me, the Expy pulled it just fine, worked it on the hills though, as is expected for an small-block V-8 towing
I would NOT want any more trailer than I have with my 00 Expy and my rig has a 6950# tow rating. I have not weighed it, but I'm sure I'm right at the limits weight wise.
What you propose is simply too much for an 07 Expy EL, all things considered. Look for a light or ultra-light rig. You may have to compromise a little, but it will be well worth it in the long run. Of course your other option is to upgrade to a differnet TV, but if you need to take 6 people with you, your in 2500 series Suburban territory (I think they are ceasing production of those next year) or a 3500/350 "1 ton" van.
Good luck!
-Greg