#1 Forget about the manual safety on the striker fired guns like Glock. They aren't going to fire unless you pull the trigger. Keep the gun loaded and chambered and your finger off the trigger and you'll be just fine.
#2. You're all over the place. You need to calm down and think about what you really want in a carry gun. Or if you even want a carry gun because you don't sound like you do.
How do you dress on a daily basis? What kind of shirt do you typically wear? Do you wear your shirt out or tucked in? Do you wear jeans, slacks or shorts?
How you carry this firearm will be greatly dictated by how you dress on a daily basis?
What size and/or type of firearm you should carry are going to be largely dictated by how you dress AND how you are going to carry on a daily basis.
You mention shoulder holsters a lot on other threads but unless you wear a suit or other type of jacket daily they aren't practical.