get as many as you can, sell them to have the money for what you want in your shop. Most shops up to about 800 sq ft do well with one pair of speakers sitting on shelves. If you have a 3000 sq ft shop then get two pairs. You don't need loud sound in a shop, it will not be pleasant after a short while when you are trying to concentrate on doing something. You want background music. I love music and prefer it to TV / home theatre. I ran a store for a big US audio store chain many years ago. Trust me. You do not want music blasting in your shop nor do you want the hassle of having to ceiling mount speakers all over the place unless the building is big enough for, "Clean up on aisle 9" announcements.
I don't know, I like loud music in my shop when I'm doing boring things. If I'm trying to concentrate on a diagnosis, I want quiet. But if I'm just changing oil or sanding/painting, doing scrap teardowns, whatever, I blast away.
This has kinda been a constant theme around here when the topic of garage stereos come up. Some just want ambient music, some want to party.
I personally like a little of both. At one time I had the full-on Doc Brown setup with multiple amplifiers, 21" subwoofer, speakers all over the place. It was fun. Now I've moved into a tiny temporary shop, and all I have set up at the moment is a little 2.1 PC speaker set. It gets the job done in my microscopic shop for now. But when my big shop gets finished, I have 4x 15's and 2x 18's ready to deploy, along with a 70v setup for the driveway/courtyard area, lol.