Thanks so much, folks. I was trying to put off posting about the event until the results were online, but no such luck so far. Goal #1 was to finish. Check. Goal #2 was to not finish last. TBD (I'll follow this up if/when results are posted). The challenge went exactly as the last email stated (and as I last posted). Some items of note:
--I weighed in at 200lbs with all my clothing for the run, meaning my pack had to weigh 20lbs. It weighed 24lbs. I think the pack on my practice run was 10-15lbs. I know to drop a brick (4 x 4.625lbs for this event) next time as we weren't allowed to alter our pack weight after weigh-in. That hurt

I'll also monitor my bodyweight more closely next time as I carried a few extra of my own pounds from a month of not really tending to my diet.
--My 5K blew as I lost perhaps a minute or two to walking, finishing in 37:49 (from what I vaguely remember while staggering across the finish line). I don't blame the weight so much as the hour leading up to the run, during which we were made to literally stand around in an open field (wind chill right around freezing) waiting for the whole thing to get started. I won't complain too much since this was the first time for this event, but we weren't allowed to remove our packs after reporting in, and there's only so much warming up I could do with that weight on (I'd foam rolled and done some movement prep before leaving for the event maybe three hours before that, so not much benefit there).
--I ended up with 16.9999999 push-ups (suck) and 45 sit-ups (surprise). Still waiting on the PT and overall times. I would like to say for the record that the vast majority of push-ups and sit-ups I saw performed were half-reps, but I did the full ROM, so they can all suck it

We had to stand in line for about twenty minutes between the run and the PT, so that recovery certainly helped, though my quads got really tight in the interim.
I have a lot of push work in all planes and areas--especially for reps/endurance--to do before another event like this. My arms especially need some attention, which seems counter-intuitive for me since I've long held the opinion of focusing on full-body (read: big muscle) development and letting the distal muscles develop in concert rather than doing isolation work, but let's face it: I have weak arms. Perhaps I've either compensated for or avoided certain movements all this time (my pull-ups suffer more from inadequate upper arm and grip strength than from anything else). I also feel the need to go back to squats and deadlifts for reps (~20 per set), and I can continue to use this weighted pack for running/sprinting until I can afford a proper weight vest. I'll be surfing training programs for the next couple days until I find something that seems to address my needs.
The next event is May 3 at the
whitewater center--apparently there is an on-water element involved, which will be cool--so I have about three months to prep. I really wanted to go through Core Performance again, but I have a feeling I'm going to need something a little more strength-centric in the gym while getting back to running 5Ks with a little more regularity (trail runner suggestions, anyone?)

My track work will remain as-is (once every two weeks or so, maybe a little more frequently). Hill drills need to be more involved. So many areas/issues to address...
FWIW, my partner wore a 16lb pack (only needed 14lbs), could've done the 5K without stopping (had to stay together, so I slowed us down), did 14 push-ups, 45 sit-ups, and we matched all the PT stuff per the event's requirements (except that I carried her both times across the field). I'd also like to mention that we raised an additional $250 (totally unexpected) in donations, so that was pretty cool. Still awaiting official race results...
EDIT: I forgot to mention my current physical state. Quads are sore but nothing major. Chest is moderately tight, again nothing major. My back is oddly sore, perhaps from carrying that pack for as long as I did. My shoulders are oddly unaffected; hopefully that means I loaded and wore my pack appropriately. I know my running form suffered from both the weight and trail terrain, but a lighter pack in the future will keep my form as it should be, so no worries with that. A little rolling and stretching today, and I'll be ready to hit it again tomorrow.