Oh hello there, i checked back in at the right time. To answer your questions based on my experience as a pipe smoker of about a year in earnest after transitioning from cigars:
1 - No, unfortunately there's not a lot of money in that. However, I had great success at Pipe Smoker's Forum with getting a sample bag, and I would be happy to do the same for you (little sample sizes of multiple different stuff). If you're interested, shoot me a PM and tell me what kind of stuff you're interested in trying. I have come to have a stupid amount of pipe tobacco.
2A - Yes, I sometimes pack half bowls. In fact, it is often recommended to break in a new pipe by starting with a few half bowls to establish a char at the bottom.
2B - No, relighting a pipe is much more forgiving than a cigar. IMO, a cigar should be re-lit within 15-30 minutes or chucked unless you trim off anything that was burned and immediately re-humidify the remainder. Pipes, on the other hand, can sit for hours or even a day or two without serious impact, and you'll have no problems with flavor, I've found.
3 - Welcome to the biggest challenge in pipe smoking. After about a year, I can now usually get a pipe to stay lit well about 75% of the time. It's all about experimenting with different tobacco, your pack style, and different pipes. The classic combo for learning how to get your light and smoke down pat is Carter Hall in an MM Cob - I did it with a little Eaton, but any cob will do. Long and short though - different things work for different people, and it's part of the mystique of smoking a pipe. Some guys will just pack via the old "codger scoop" and that's all they do. I can't do that worth a crap, but the "reverse gravity" method (inversion of the bowl rubbed over loose tobacco in the hand) works best for me. I have never had a filter or stinger impact my light or smoke at all.
Also, to address another question you had above - a tight pack is your worst enemy, mostly because it'll make the draw too snug. This is why everyone always says to tamp "with the weight of the tamper", and not to apply any extra pressure.
Cheers man, and enjoy the piping!