A few dead bees anywhere is normal. Beginners always fret about everything. I know I did. Next year you'll be laughing about how concerned you were about nothing. Anyways, a liter a hive in 72 hours is a pretty good amount, especially if its raining. And yes, they will push the bees off the entrance board when it is a nice sunny day, who wants to get wet?

Good luck with your first inspection.
Jake