first and foremost welcome to the site and your right to keep and bear arms.
For me I dont have a preference for a semi over a revolver or the other way around. I myself will only carry a weapon condition 1 and no thumb safety even if you carry with the thumb safety in fire it could get bumped through your day and be on when you need it, but thats my opinion. I have a sw99 and a xd both are in 40 and 12 round mags. My wife has a J frame 38 spl +p hammerless (636 i think) either way its nice and I love it but its hers so I'm not allowed to buy a right handed holster for it
(im right handed and shes a lefty) 38 spl +P is plenty for that weapon and a wad cutter or hollow point behind that is ballisticly enough for SD.
As already stated just as important as the weapon is the holster you choose. It should cover the trigger and prevent the weapon from being able to be fired (pulling the bang button) while its holstered. It should also be comfortable for you to wear or you wont wear it and it should be comfortable and a natural motion for the draw. there are too many holsters to name but some of the more popular ones are crossbreed super tuck or kholster and blackhawk serpas
Also once you have everything you think you need practice practice and then practice, not only with your weapon and holster but with your carry ammo. Make sure the ammo you choose to carry will feed through your weapon properly. When I find my self trying a new carry ammo I buy atleast 2 boxes (one to shoot and one to carry) for everyday practice I buy the cheaper stuff until I get my reloader setup.
"The purpose of war is not to die for your country. The purpose of war is to ensure that the other guy dies for his country." - General Patton