OK.. that's a start.   Here are some thoughts on what you are thinking about so far.
Face Painting takes a long time to do..   average 5 minutes a student,  perhaps?  We used to have face painting at our  Fun day, and  kids spent a lot of time waiting in line to get it done,  when they could have been enjoying other activities.   Then, there's the issue of paint on the clothes.  Lastly,  there's the issue of  hot, sweaty kids and the paint runs.
I would opt for buying the  press-on-with-water and a sponge  "tattoos".  You can get them VERY inexpensively through 
	www.orientaltrading.com
   and they offer a wide selection.   We buy the big assortments,  and then pull out a few that may not suit our public school  ( like crosses, or skulls).
Doing the tattoos is easy, and fast,  all you need is tubs of water and sponges, and several kids can  do it at the same time..  no lines, no waiting.
Next,  on the " awards ceremony"..  if your school has been struggling, perhaps rewarding honor role kids would  be a good thing.  However,  in my opinion,   it doesn't seem quite fair to celebrate 30 kids on a day when the hard work of 380 kids should be rewarded.  Perhaps a big posterboard with their names on  it would be enough??   This thought depends entirely on the  philosophy of your school.
Last,  on the BBQ.  Does your school already provide a food service?  will you be buying the food through your school dept?  ( it is MUCH cheaper this way)..   Will you rent grills?  Are you allowed to have propane or open flames on your school grounds?  WIll your health dept allow rented grills or grills from home?    Will your school cooks do the grilling, or are they contracted to only do their part in the kitchen?  Do you have any parents who  have food safety knowledge, who can be sure all foods are cooked to the safe level??
I know all those food questions seem ridiculous.. but all it takes is for ONE thing to go wrong, and some parent will sue your  city or make a big stink about you not following procedures.  It's better to get ahead of these issues  and know exactly what  you need to do.
On the admission price,  I think it's a bit tough to " charge admission"  per se.  What you could do, is send home a nice flyer  saying that in order to pay for this event,  students are being asked to contribute xyz $$  toward the cost.  You could add  that any leftover monies will be carried over for next year's  event.
more later!