BOMM melomel

I've never done a BOMM but from what I understand you can do this.

You asked about degassing and aerating. Did you mean in the 5 gallon primary bucket or in the five 1 gallon jugs? The main risk of overflow will be early in the primary fermentation. If you have 5 gallons in a 5 gallon bucket, then yes, you should worry about overflow. A 6 or 6.5 gallon is recommended. Once you rack the mead into 5 jugs, you won't have much room left to add fruit. There might still be some fermentation taking place with the new sugars added from the fruit (unless you stabilize with sulfite and sorbate). But at that point you don't need to worry much about overflow, and not at all about aerating.

Have you considered modifying the recipe down to about 4 or 4.5 gallons, then you can split out to 5 jugs and have room for fruit?

EDIT: With regards to timing, I would recommend keeping it in primary until fermentation is complete (it reads 1.000 or lower on your hydrometer) and then racking.

I’m no expert, but it probably depends on the fruit. Some people say as little as 10 days. Some say several weeks. Too long and the fruit can start taking on a “vegetal” flavor. Probably check it every other day and see how it smells/tastes.

Are you aiming for a sweet or dry mead?

At some point I expect you will stop fermenting all together in carboys and swith over to buckets. At that point this will then become a non issue.