1- Do most people who carry concealed semis, carry a live round in the chamber?
This is generally the prefered way. Condition 1 or 2 both have rounds in the chamber...
Let me ask you this - Are you comforable with a Revolver with all 6 cylinders loaded?
If NO - then Condition 3 (loaded magazine is seated in the handgun but the chamber is empty) is your best natural option.
If Yes - then we can move on. The thing about the Revolver is simple... If the weapon is loaded - Dont be pulling the trigger. It is very safe - until the trigger is pulled to the rear. Modern Autopistols are the safe way - they are safe until the trigger is pulled to the rear.
If you are more comfortable with the Revolver style - a DAO auto is certainly the way... the trigger works just like a modern Revolver.
I carry Condition 1... This is a loaded mag and a loaded chamber with the weapon Cocked and on Safe. I carry a 1911A1 Springfield - This weapon has 3 safes and will not fire until I defeat all 3 and pull the trigger to the rear.
Okay - my bad - One of those safeties is a trigger safety and wont allow a fire until the trigger is pulled. I am comfortable with these features... hence I am comfortable carrying this way.
I also have a Detonics Combat Master that I carry often. Its a chopped down 1911 that only has 1 safety. This I quite often carry condition 3 as I am not fully comfortable in this weapons features. The thumb safety is secure - but there is no built in back ups to it. When it gets dark or I'm in the city - I move to Condition 1 carry mode until I am in a lower threat area.
With a 1911 - Condition 2 carry (a loaded mag and a loaded chamber with the hammer down) is totally ill adviseable. Dont do it. Because one the new guns you have only one safety and on the older guns you dont have any safety and an impact could fire the weapon.
2- I understand the concerns about accuracy and adjusting for trigger pull on the single/double action autos, but what type of safety mechanisms exists on each and what are the pro/cons of each.
This depends on the specific pistol... differnt makers have different systems... Sorry - not general answer for this.
3- What about hammerless semi-auto (Glock, and Kahr P9 come to mind) how does the safety mechanisms work on these type of guns and pro/cons of each?
These types of guns (generally) have 2 types of safetys... One is a firing pin or striker block that keeps the striker or pin blocked from movement or out of alignment with the cartridge until the trigger is pulled to the rear.
The other is a trigger safety that doesnt allow the trigger to be pulled until the safety is pulled off first - like the Glocks little lever thats on the trigger or the lower hinged portion of the trigger on the Sigma. I believe Kahrs safety is in the first little bit of the trigger pull its self - but I'm not sure... I dont pay attention very much to the kahr. My wife had one but I only shot it twice. (It was a 9 and I dont groove on Nines...) I could look the Kahr's system up - but I am lazy...
4- Reliability is another concern. I want a pistol that I know will shoot when needed, can be shot a lot, and is not real sensitive to my choice of ammo. Is there a specific design type that seems to be better than another?
Yes... a revolver.
Revolvers dont depend on the recoil or blowback of the shell to cycle the action. Autos do, so all autos are sensitive to this to one degree or another. Even so - this can be adjusted by replacing the spring... So its kinda not relavent the sensitivity issue. General reliablity is a big concern however and one to take to heart. Accuracy is nice - but in a defensive pistol not a great concern.
In your previous thread and again here - the Sig series was suggested. Sigs are Right on the top of my list. They are also a bit spendy compaired to more pedestrian offerings.
Look for a gun of good quality and with a history of reliability. The Sig pistols have a unique action - you have to get your hands on one to appreciate it.
HK USP Compacts are also very reliable and sturdy - very safe... Another good option.
There are so many good options for a possible auto... It really comes down to personal taste and comfort level.