^ Ditto on that sex-drug comment :D
As for insufflated dosage, it appears to be all over the place. Some people trip hard from tiny bumps while others need huge lines. I am at the upper range of it as well.
The way I approached this when I first tried DPT is as follows: I made a bunch of lines about 50mg each, then insufflated one, waited for 15 minutes (about how long it takes for the effects to peak), then sniffed another one. 15 minutes later, I was feeling pretty intoxicated, but still no visuals, so I took another line. Soon after I was propelled deep into the DPT space.
In retrospect, doing 50mg increments might not have been the best idea, even though it worked out fine for me. I think it would be wiser to do them in 25 or 30mg increments instead, starting with 2 lines (or about 50mg) - that would allow for better titration. Once you find your dosage, however, you can measure it all out and do it at once the next time.
I think the drip is pretty nasty with insufflated DPT, but nothing too unbearable IMO. It does leave your throat sore for a day or two, so if you have problems with your sinuses it might be a good idea to avoid it just in case.
Regarding rectal dosage - it's pretty wasteful IMO, but if it's your only option, I say go for it. You will need quite a bit more of the substance than insufflated, however.