Don't stress the small stuff. Smile, have fun.
If you are going to work on fronts don't do them as part of the recall. You don't want to mess up your recall in the process.
What I did with Donovan when he thought he should sniff is I had a long line on his pinch and when he started to sniff or think about sniffing the long line tightened. If he moved he was put back into position and we started over. I also did this for his getting a bit whiny when the other dog did the retrieve. Whining and/or sniffing are not part of the down. I have used the E a bit with Deja, nick, if I notice her neck getting a bit long during the recalls and/or retrieves or if she starts air scenting something in the bushes along side my field. She is very solid in the down, though, so this was brought in later mostly as a reminder to keep her attention on me in the blind and not other things. I have never used it to make the down solid. I prefer what I did with Donovan for that.
There really isn't any way to prepare for the traffic portion since the judges tend to vary what they do. Just make sure he is comfortable around other dogs, traffic, joggers and bicycles. Also, if he is chipped, make sure he will stand and allow someone else to scan him (sometimes the handler does it, but not always). If he has a tattoo, make sure he is comfortable with you showing it. Walk him around in a crowd. Make sure he will stay quietly tied out with you out of site. These are the things I see most commonly in BH.
I have done 7 BH. I hate them because IMO they are a waste of my time, but they are required. As long as your dog is fairly obedient and doesn't do anything majorly stupid you will be fine. In the ones I have done, Elena had down on the brain, Donovan forgot his front all together and thought he should do a send out on the build up for the down in motion, Deja did a gorgeous stand in motion instead of a sit, Vala about took me off of my feet on the recall, I fell between the fast and slow on both Nike's and Treue's heeling patterns and when I did Tara's I held my hand up in front of my stomach like we did in AKC and the judge asked if the dog thought I was hiding food.
I have seen handlers turn into strange zombie creatures that their dogs don't recognize and they still manage to pass. You will be fine.
Who is the judge?