Yep, it looks like you fired up all of the lump at the same time.
Minion method is your friend. Once mastered, that huge arse basket should burn for over 24 hours.
When using a UDS, fill up the basket with unlit coals (well maybe in your basket's case, 2/3 full) with your wood chunks buried at varying depths within the unlit coals.
Start 10-12 briqs, or briq sized pieces of lump in your chimney starter. When they are completely ashed over, dump them on top of the basket of unlit coals/chunks. Wait for cooker to stabilize at desired temp. I like to start cooking @ 250. And when I say stabilize, I mean thin blue to invisible smoke.
It usually takes 15-30 minutes max for this to happen. LEAVE ALL intakes open till 25 degrees below target cooking temp, then close off all except one. When target temp is reached, close off the remaining open intake to 1/2 to 3/4. This should get you close to what you are seeking.
If you do that, your problems will be solved.
BTW, if your PVC exhaust pipe melted, it must have been raging. Possibly raging enough to kill your thermometer.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)