Unless this is some sort of enjoyable, hypothetical armchair exercise, many of these questions require some exposure to properly conducted training in order to get some meaningful answers.
Carrying and moving about in the real world while holding a handgun can expose the armed person to a myriad of situations, ranging from those imaginable to probably a surprising number of them haven't been considered. The world and how its events unfold is hardly ever scripted to our expectations, right?
Only knowing how to hold the handgun in 1 or 2 pre-programmed techniques, and counting on always having both hands available to devote to the gun, may not provide someone with enough tools to face some real-world problems.
Training often answers a lot of questions, including questions someone may not have known needed to be asked prior to the training experience.
Understanding basics is always good, but learning how to safely, properly & effectively apply them in a variety of situations, and how to change according to the demands of the moment ... especially while under stress ... is probably best learned under the watchful eye of an experienced instructor.
Learning martial arts via the self-taught method, whether from books, magazine articles, video clips or DVD's, is still not nearly as effective of a method of learning as hands-on training under a trainer. Useful as a supplement for the learning process, sure, but not as a replacement for actual training & supervised practice.
Mistakes and bad habits are usually hard for the practitioner/student to spot for themselves.