Kegging mead

[PNP]

1st time making mead... Couple questions.
1. Planning to make 5 gallon batch. When I rack to carboy, how much head space will there be? Is it worth adding a couple more lbs of honey and making 5.5 or 6 gallons?
2. I'd like to make 1/2 still and 1/2 sparkling. Is there anything wrong with putting 2.5 gallons in a 5 gallon corny keg?
Thanks!

 

[RegarRenill]

I make 5.5 or 6 gal batches for this reason. What doesn't fit, I put in smaller jug or bottle for additional topping up later.

 

[MarshmallowBlue]

2. You'll use more Co2, but that's about it.

 

[Duganson]

Since you are kegging and you likely have CO2 tanks laying around I would suggest just dosing the head space once a week with your CO2. Its what wineries do with tanks, headspace or not.