Red has given you very wise info on the Queen n container you’ll find in your 3 boxes of bees.
I also started 3 hives this season. I chose to use Nuc’s as I wanted a quicker build up of the colony. Back when I was a teen we all started with packaged bees or swarms.
As Red mentioned … Take your time. Do each hive slowly n carefully one at a time. And please enjoy the ride. As for adding an additional frame, I wouldn’t. If need be you could add what is called a follower board to use some of the extra space until your colony gets the frames built/dawn out on the two wall/outer frames. I am not using a Flow-hive n I do use wax n plastic foundation so weren’t not exacting talking apples with apples experience but close. I’d just push/push your eight frames tight together/shoulder to shoulder n center all frames with equal extra space in out wall area or push to one side n add a follower board to use that extra space (the board needs to be same as other frames dimension length n height wise). Thickness less than a frame … Keep it simple as its only temporary n removed as wax is drawn out later. .
Here’s a couple of not exact examples I took for you. My example is using a standard 5 frame Nuc-hive but the idea is the same. Push frames offsides/to one side …
. Then add a narrower follower board. ( I didn’t have time to cut an exact - sorry - this morning so it’s pretend !
. There’s a couple of pix’s of my small apiary here in my backyard here SE of Seattle.
This WRC on the right is a standard 10 frame I bought from Beethinking.com
who builds the Flow Hive.
. Again as Red n others will repeat … Take one hive at a time. Have an ice tea or something if you feel overwhelmed n your nerves n brain waves will return to normal … Then back to the next package n hive until DONE.
Enjoy n good luck,