Steve
I will answer the easy one first.
Non-stick indirect cooking - When I roast or cook indirectly, I use either a Weber Aluminium drip tray if I think it is going to be messy - it is easy to just throw them away. If I am going to do a long cook with low heat, (temp control turned to minimum) or I know it is not going to be messy I use a non-stick pan with a rack on it. I bought a couple of cheap ones from a home catalogue here in Australia for about 10 bucks each. Yes, the heat does affect them a bit – to overcome this problem I put a doubled up sheet of foil underneath the tray. Seems to fix the problem and work OK.
Cleaning - you will probably get a variety of opinions all of which will work.
This is my cleaning regime. After cooking and while the grill is hot I brush down the grill with a Weber "D" shaped brush this dislodges most of the gunk and gets it reasonably clean. I then wipe down the lid with a cloth to remove any splatter. After the meal is finished, (and to get out of clearing the table and washing up) I remove the grill and wipe out the bottom of the Q, removing the majority of the gunk. I then wash out the drip tray and pack it up. Total cleaning time is about 5 -8 minutes.
I always preheat on high for 10 minutes before cooking this will burn off any remaining gunk, I then give it a quick hit with the brush again close the lid for a couple of minutes to bring up the heat again and them I am ready to cook.
Every 2-3 weeks or about 10 uses I take the lid off, remove the grill and drip tray and spray it all over with some normal washing up detergent. I leave this for 10 minutes and then wash it down with my high-pressure washer (K'Archer). I then turn it upside down for 10 minutes to drain any water out of the burner ring. I then wipe it down, re-assemble without putting the grill back on, light the gas using a gas lighter rather than the igniter, check to see that the burner is properly alight (if it isn't just wipe it over where it isn't with a rag and it should light up) I then put the grill back, close the lid and leave it heat up for 10 minutes. - all done in about 45 minutes.
If it is exceptionally dirty I spray the Q with easy-off oven cleaner instead of the detergent - but not the grill. I leave it for 10 minutes and clean as above.
To preserve the grill when you have heated the Q for 10 minutes after cleaning spray the grill all over with some vegetable oil and then let it cool down. As it is cooling, it draws the oil into the cast iron instead of moisture and preserves it.
Regards