It certainly does sound lke he is healthy and with a good weight. Brumation won't be a problem for him at all. He will lose a little weight but it shouldn't be drastic. When my female brumated, she lost about 25g or so. But she was around 300g before she brumated for the first time so I wasn't worried abut the weight loss. I knew that was what she was going through as in the apartment I was in, it wasn't very well insulated and as I paid for the heat, I didn't want to have a huge heating bill each month by cranking up the heat. So that difference in temperature was what put her into brumation.
During the 4 months my female was in brumation, she would come out for a few hours or most of a day (I worked a later shift in the day so many times when I woke up late morning she was already out basking, so I don't know for sure how long she had been out). Typically she came out every two weeks or so, give or take. I don't think there is any need to dig your dragon out to mist. In the wild they won't be misted as they are not lying out in the open where morning dew or rain can reach them. They are buried in small dens, under logs or rocks etc. It is fine to give her a misting after she comes out on her own for a bit of water. Small amounts of food can be offered, but you don't want to really fill them up as you want the food to be completely digested before they go back to brumating.
Not all pet store employees know alot about the proper care of the animals they sell. Some are more knowledgeable than others. Forums like this one and online caresheets are a great reference, despite conflicts between sheets. ALot of information on the internet is accurate but also, alot are older and out of date or just plain inaccurate, as the publisher of the caresheet may not have done their research very well, if at all. Or it could be an old method that they feel has worked for them, or a new method that is working for them so far.
Also, the petstore owner may have decided not to mention brumation as not all bearded dragons do it in their first year. She/he may have felt too much information right away may be hard to remember and was more concerned you have the basic care requirements down pat. Things like basking temp, uvb etc. THis particular petstore employee seem sto know his stuff, so it was good to check in with him again about this new development in your dragon. Not sure how his other information was accurate but he was right about the brumation 
The only bad thing about brumation, is you don't get to see him/her every day and interact with him. I noticed th at with my female, after a couple days of not seeing her looking at me through her cage and doing her other peculiar activities, I missed her. Even now, having had to sell her about a y ear and half ago due to moving and not having a place to keep her comfortablely for 2-3 months while I looked for a new place, I stil miss her. Eventually I wil be getting another bearded dragon. Th ey just have too much character not to have at least one in my collection of exotics.