Happy if I can help. I wish I had known a lot of stuff like this with the first dog. That was no fun at all cleaning his diarrhea accidents off the carpet in those first couple of weeks. Ick.
A half a tablet a day for a Beagle should be good. Though I got my dogs as puppies they're large breed dogs and roughly Beagle sized when I got them. Yoshi was already huge since I got him at four months of age and he's on the biggish side for a male Akita but I still just gave him half a tablet a day and he was fine though he probably should have taken a whole one.
The tablets are big so they're easy to just break in half. And I gave it to him about an hour before his chow time of the day (I split his food for the day in half and feed him twice a day... seems to have better digestion that way). I kept him on them for the first week and a half... I was told he should get them for a week or two, so I compromised and did a week and a half. It's kind of funny that at the end of that time both Yoshi and Boo before him felt cheated out of their little pink "appetizer" before their meal, and I felt like a meanie when after that week and half I didn't give them anymore.
I don't think they come in a box smaller than 30 tablets, and the dog will need only a few of them, but it's nice to have them hanging around since pepto is one of those meds that everyone could have a need for once in awhile. There were a few times I was very glad to remember I still had the rest of them long after he didn't need them anymore for my own occasional stomach complaints.
So, tomorrow is the big day you bring your new fur-kid home! I was always so excited about getting each dog I couldn't sleep a wink the day before.