Experienced cutters are probably using unfamiliar words to describe what they're suggesting. I'll try to clear it up.
To answer your questions; You have a couple of options. Of course, cutting from both sides is a common solution to this very common problem. The
kerf, is the slot created by cutting. When you get close to the bottom the wood can sometimes shift and start closing the kerf, which pinches your bar, creating a lot of cussing that you never knew you had in you. A plastic wedge solves this problem. You can get them from Bailey's. They're cheap and WELL worth the expense. I must use a wedge a hundred times a day when I'm cutting. Get the plastic one because you don't ruin your chain when you hit them with the chain. Kiss your chain goodbye if you hit a metal wedge or your axe blade. You can get to Bailey's by clicking their icon above.
If the logs are really big you might need a cant hook or a Peavey to roll them over. I prefer the Peavey myself. If you're going to cut a lot of wood either of those would be a good investment, but they can be a little pricey.
Here's the most important part. You asked about burying the bar. There's no problem with that, as long as your bar is getting plenty of oil. The 455 can handle a 20" bar all day long without a problem. The thing you have to be careful about is kickback. To say that kickback is dangerous is an understatement. People have been killed or horribly maimed by kickbacks. The best thing to do is avoid using the top quadrant of the tip of the bar, (9:00 to 12:00 or 12:00 to 3:00, depending on what side of the bar you're looking at), to cut with. If the chain catches there it throws the saw up, usually into your face or your leg. If you have no choice other than using the top part of the tip, be sure to hold on tightly and be ready for a kickback. You won't stop it from happening, but hopefully you'll catch it before it cuts your jugular vein.
Something else you might consider is Personal Protective Equipment. Always wear safety glasses when cutting. The other thing to look at is a set of chaps. They'll stop a chain before it cuts through your leg. Go to
www.labonville.com and take a look at what they're got. I think they have the best chaps. All the other vendors carry chaps as well. Even if you don't get the best, something is better than nothing.