Ok, you will probably get some different answers to your question. We all have developed our own way of doing things. Here is my way. If I am doing an unlined holster I use 10 - 12 oz ( 9-10 oz will work if that's what you have)veg tanned leather. If I am doing lined I usually use two pieces of 5-6 glued together and worked as one piece. If your doing unlined draw your pattern on your leather and cut out the holster. If you are doing lined, draw your pattern on the leather (5-6 or 6-7 oz). Cut out the holster. Turn the leather over, lay your cut out holster on the piece of leather ( in an area you want to take the second piece from) the leather should be fuzzy side to fuzzy side. Draw a line around
the holster on to the leather you are going to cut. now apply your contact cement inside the line covering the entire area also apply glue to the back of the cut holster. When appropriate (follow direction for the glue) align the two pieces and press together.
Once you have the holster cut out and ready here are the steps I do pretty much in the order I do them. Not right way or wrong way just my way.
Cut out slots for Mexican loops.
Dye- Before dying I recommend you take a scrap of the leather you are using and dye it, let it dry. This way you can see if the color is going to look the way you want it or if you are going to have to thin it. Once you have it looking the way you want the color dye the holster. Let it dry 12 - 24 hours.
Here is where you will get some variance. After I dye I oil. Some people use Neetsfoot oil some use olive oil, some use a conditioner. I use Pure neetsfoot oil (not compound). Let the oil migrate through the leather 24 hours.
Lay out your stitch line.
Titch the holster. If you are doing lined holster you will want to stitch the entire perimeter of the holster including the skirt. On a lined holster stitch all areas to be stitched except the main seam area. When ready stitch the main seam ( I Usually glue my main seam first let dry 12 - 24 hours then stitch the main seam.
Now here is another area the process may vary. I run the holster and skirt under the faucet get it wet it should all look pretty much the same color. Take the holster and tuck it through the loops pulling it so that it is seated where you want it. Now take your gun wrapped in plastic or what ever steps you are taking to protect the gun and push it in. If the holster seems tight and you have to fight a little bit to get the gun in that is a good thing Keep pushing until the gun is fully seated. Shape the holster to what ever extent you want I usually just do a general shaping no detail molding on western holsters. Flatten the skirt and shape as needed. Let it dry a little bit. Now I take the gun out of the holster and put it in the oven at 170 for about 10 - 15 minutes this helps dry the holster and give a bit firmer holster there are some other things that affect the holster I won' go into those right now. Just letting the holster dry naturally will give you a fairly firm holster as well. Some people use a fan to blow air over it. After the oven I put the gun back in the holster for a while to make sure it has taken the shape then I remove the gun and let the holster dry naturally at least 12 - 24 hours. You should have a pretty well completed holster. However now is when I apply the finish. Some people use an acrylic such as resolene some use other products. I like to use Skidmores leather cream. I let dry 24 hours between applications with a little buffing in between each application.
I know this is a little long winded but hopefully I have answered all of your questions. I am not telling you you have to do it this way this is just my way and my answers to your questions. I hope it helps. If you are on face book you can see some of my work and see how my finished products come out. My FB page is Camano Ridge Custom Leather.