Hi, Mordent. Welcome to DC
You actually don't need a lot of liquid in a slow cooker because the process of slow cooking brings moisture out of the meat and vegetables. Deglaze means to add liquid - it can be water, wine, broth or stock - to the pan after browning and simmer it, scraping up the browned bits with a wooden spatula. This adds a lot of flavor to the pot roast.
I would marinate the meat overnight, then pat dry with paper towels, heat some olive oil in a pan, and brown the roast well on all sides. Meanwhile, clean and slice the onion and cut about 1 pound of the potatoes into 2-inch chunks. Leave the baby carrots whole.
Put the onion slices in the bottom of the slow cooker, put the roast on top, and add the beef broth. Nestle the potatoes and carrots around the roast. I don't think you need additional water; the liquid only needs to come a couple of inches up the side of the meat. I would save the chives for garnishing after it's done; they won't add much flavor and won't look nice after cooking for 8 hours. Also, I think adding raw bacon to a slow cooker will make the dish greasy. If you want to add bacon, cook it separately and add it at the end.
Since a slow cooker cooks slowly
, people generally add the vegetables at the beginning. 30 minutes in a slow cooker won't be enough time to cook them.
Here's a site with lots of slow cooker recipes: A Year of Slow Cooking
Hope this helps.