The big thing with carbon bars is following torque spec. Unless you've been installing bars for years on a regular basis you shouldn't even try without a torque wrench, and if you have all that experience you should still use a torque wrench. Getting the stem bolts right is critical. The Ergons should be safe, they usually use a clamp ring, just snug the bolt lightly. Unless the bars specify that they are designed for bar ends, you can not use a mirror and have to use the plugs as directed. The ends of the bars are usually a touch thin and have a greater chance of cranking if the plug isn't there unless specifically designed. Carbon bars are nice, I like them on my gravel bike, but they have their limits. As to cutting them, wrap where you want to cut with tape, draw your line and use a very fine tooth or carbon specific blade for a hacksaw. Carbon bars can be cut if done right.