Re. oil change interval. The only way to know your oil load's condition for sure is to have it analyzed. There's a number of outfits that do this. I use Blackstone but I don't know if they are any better than the others. Just be sure to pay the extra couple of bucks for the TBN (Total Base Number) so you'll know how much detergent is still in the oil.
The center of Internet oil knowledge is BITOG,
www.BobIsTheOilGuy.com. I know that sounds silly, but it was the tribologists that made it up, not me.
Our fathers changed oil pretty often because the engines were dirty and the oil not much good. As oil and engines improved oil change intervals (OIC) should have gotten longer but oil mfrs have marketing depts and they kept pushing the school of short OCI's. The problem with short OCIs is that 1) They are expensive and 2) They are tough on engines because fresh oil leaches a bit of surface material until it gets "mature." Then auto mfrs started paying for oil changes and suddenly OICs went to crazy long intervals like 15k miles which resulted in gummed up engines and PCVs. The right answer for OCI's depends on how you use your truck and your oil choices. The only way to know for sure is to send a sample out to be analyzed. My suggestion would be to send an oil sample out when you were figuring it was time to change your oil, and see what the lab report says. Maybe your oil has another 5k in it. Maybe 10k.
Oil choices. This is hard. Oil is like religion. Everyone loves what they use and few have hard info in support of their choice. The web is full of silly comments like "my engine loves WD40" or, "I've always use Castrol and I've never had problems." It gets worse. What was true about an oil last year isn't necessarily true about an oil this year. Some years ago, based on an old TDR article I started using Valvoline Blue in a BMW race car. After a couple events I sent an oil sample off and the results came back very different from the article. What I learned is that oil additive chemistry can change at any time. It can even change faster then the oil mfr's website so you can't even believe the official specs that you read on the mfr's site. All you really can believe is oil analysis.
If you're really interested in making sure that you're using a really great oil, spend some time searching around BITOG. I don't have a recommendation for you because I've not spent the time on BITOG reading up on diesel oils. Right now I put Shell Rotella in my truck, mostly because it's available, it's cheap, and I know from a small amount of research that it's not awful.
Synthetics vs. Dino oils. Synthetics do have some charms but for most folks the additional expense is probably not warranted. Synthetic oils handle high heat well. The turbo can get the oil pretty hot, but a diesel engine has such a large oil reserve that it should be an issue as long as you're monitoring oil temp for unusual behavior. Synthetic oils handle multi-viscosity well. A dino oil requires more viscosity modifiers than a synthetic oil. Those visc modifiers wear out, so a 10W40 dino with it's worn visc modifiers will be thinner 10k miles later than a 10W40 synthetic. The average person doesn't care about those issues much so for many people full synthetics might not be worth the additional cost.
Oil filters. There's some good oil filter studies on the web. The quality of the filters vary quite a bit. OEM recommended oil filters are pretty good. I personally know of no OEM recommended oil filter that is crap.