Answers to an awful lot of your questions can be easily found in the 'back pages' of the 'NCOWS' forum and the 'Historical Society' forum.
Same's true in the Time-Life series 'The Old West' and many, many other references found at your local Public Library.
In these references, you'll find a marked difference between the 'real' Old West and the 'reel' Old West, and you'll soon see that anything seen in the 'John Ford Reference Library' bears little resemblance to what was worn, carried and used during the era.
Ask them to get you a copy of Rattenbury's 'Packing Iron' on an Inter-Library Loan.
The cap and ball revolver was common after the Civil War - but was fast superseded by a cartridge revolver, since it proved more reliable and weatherproof to the user who would be carrying it.
A cap and ball may've seen service in a desk drawer - for the townsman.
The shoulder holster came into popularity in the very late 1880's - early 1890's, for the most part - the era when the 'Wild West' had become 'tamed' and open carry was looked down upon by the up-and-comers who saw it as an anachronism.
Of course, open carry never went away - but in town - there were laws against it and that was the heyday of the pocket revolver and the shoulder holster.
Again - look through 'all' of the 'back pages' of the two forums - once in awhile, the headings can be misleading, but questions on clothing, weapons, time frames, et al, - have been asked and answered and referenced, and many include links to sutlers and suppliers.
Vaya,
Scouts Out!