I note from you questions ...you are sticking your toe in to test the waters
here are a couple of pointers to your question
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The time period/ persona im going for is what a ranch hand/ cowboy would wear when riding range for a ranch owner. That's fine, OK so now a time period....classic cowboy period was rather short, from 1865 to about 1880.
NCOWS runs 1865-1898...
If you plan a Henry , 66 , or Winchester 1873, BP frame Colt ETC> your are in the Golden era
If you plan to use a Winchester 1892 or Marlin 94 you will limit your era to the last of the passing breed.
Specifically Texas if that matters. It does climate & condition dictated wardrobe , so did cost & availability.
Not sure what would qualify best for that in regards to authenticity. Vest? sure
in the Victorian era , shirt sleeve was considered less than dressed ...a vest adds to the impression, cooler than a coat and adds pockets
something most period shirts did not have.
Choose Cotton , linen or light wool , skip 50/50 fabrics
Trousers inside or outside of boots? depends on the boots, it was done for a reason not a style...
Kept nasty critters from crawling up the leg, kept trouser out of the mud & snagging on thorns, briers etc.
Mostly Trail .... with Mid- Calf or higher shalfs ....
Bib or button shirt? Etc. Pull over Yoke styles ..... Button downs are way later in the 20 century
Bibs don't work with Vests , and are warmer to wear.
Just trying to get started off on the right foot and decrease future headache. Read the NCOWS Tally book section on building an impression.