There is a large variety in terms of numbers working in a Taylors (tailors) shop during that time, some could be only a single person or just a few, others in bigger cities could be dozens. The phrase "Nine tailors makes a man" gives you a good idea of a normal number range as well. It's not usually one person working on a garment from start to finish, but many hands specializing. The cutter is usually one of the most advanced, but the person who does the buttonholes or other finishing needs a great deal of skill as well. All of the people working in these shops have gone through apprenticeships to learn the trade. Workplaces are made up mostly of Journeymen, possible an apprentice or two, and a master or foreman of the shop.

If you want a new coat made, for example, you will most often go out and purchase the supplies yourself, more often from a different shop (that's a lot of overhead to keep a good selection of fashionable fabrics). Just like you know your size today, you knew how much fabric you needed. And not just the fabric for the outer portion, but the lining, pocketing, buckram for interfacing, buttons, thread, and button twist. Bring this to your favorite tailor (you may have a different one for breeches) and give him as much or as little detail as you want on design. You can leave the purchasing of fabrics to him, but this is how you really determine pricing. It's not the tailors work that's the costly part, it's your fabric. He'll take measures on a paper tape by putting notches into it. In theory you'll return in about two weeks (it only takes 3 or 4 days for a coat, but there's others in front of you) to pick up your finished garment, which should fit perfectly.

The process you didn't see is that the measurements were applied to a paper "shape" on the fabric. This shape is the optimal coat shape. It isn't meant to fit anyone. Your actual finished cutting shape is drawn in chalk on the fabric. Every fabric stretches differently so it's pointless to try and make a pattern for every person and every garment they want. Once cut out with large tailors sheers, the "cabbage" left overs tossed in a basket, it is passed on to a tailor sitting upon the board. They sit "tailors style" or cross-legged on this table (really a board and saw horses) to keep the fabric clean and off the floor as well as to support their back muscles and give them a good curve to the spine that won't hurt them at the end of the day. It's also good advertisement (and light) to sit in the window. For this they remove their shoes, often wearing slippers around the shop, and unbuckle the straps of the breeches at the knees. For being the providers of fashion, there's a great deal of caricature of them running down the street in this state of "undress" to catch an un-paying customer.

The sewing process is a little too detailed to go into here, but like I mentioned, it will probably go through numerous hands sitting upon the board. Every fitted men's (and some women's) garment is made this way with rare exception. Even cheap items, just made from cheap fabric. I don't have numbers for the Continent, but in the American colonies a full three piece suit in the making will be about 1 l. 4 s. (24 shillings). That wool broadcloth so popular could be a lesser quality at only a few shillings a yard, or it could be pounds a yard. You'll probably need four or five yards at least. Two or three yards of lining for the coat, a yard or two of linen for the back of the waistcoat and pockets, a half-yard of buckram, the buttons and threads; it all usually adds up to much more than that 24 shillings the tailor receives.

The tailor takes care of your breeches, trousers, coat, waistcoat, jackets, greatcoats, ladies stays and riding habits, etc. A mantua maker makes women's gowns and sometimes robes for men. A milliner will sell you all of the unfitted pieces and accessories. For men this would be your shirt, cravat or stock, work caps, stockings, buckles, shoes, pocket watches, snuff and boxes, pocket pistols, canes, swords, gloves, or anything else fashionable. They import most of this, even many of the things they could make like shirts, since larger warehouses mass-produce these items much cheaper.

So, take all of this and add in the occasional woman, usually working as a sempstress since the trade didn't often allow for women, a dog and/or cat, a canary, a few jokes about surviving on cabbage (not only because of the scrap names, but it was a common and cheap food they ate to deal with digestive issues of sitting like that all day), a fire going to heat the gooses (tailors irons), likely a bit of alcohol, maybe even some live music or reading of the newspaper, and you have an 18th century tailors/taylors shop.

Fortunately for you, in the late 18th century a Monsieur de Garsault worked on an encyclopedia of trades and skills. One of the entries deals with the art of tailoring, and it came with several illustrative plates showing the history of fashion (he did a decent job of it, too), the pattern pieces used for various garments, and the tools used by tailors. Here is his representation of a typical tailor's shop: the young apprentices seated cross-legged on a table near the window for good light, sewing; another apprentice flattening a seam; a more senior cutter, casually dressed in a robe and nightcap; and the tailor, taking the measurements from a customer.

At this time, there was still a lot of specialization - no department stores selling all sorts of premade goods. You would go to a hatter for a hat, a glover for gloves, etc. Clothing was made to fit, and unless you went to a slop shop for sailors or went secondhand you wouldn't find clothing waiting to be bought.