Re: What size to expand to next year?
Not sure of your definition of a split. For me, I remove a couple of frames of brood, a frame of honey and pollen from a strong hive and start a NUC. Experimenting with raising queens, however purchasing a queen for $25 as been the most successful.
Insert drawn comb into the brood nest of the strong hive. In 2-3 weeks take an additional 2-3 frames of capped brood from the strong hive and move it to the NUC. Strong hive thrives and by bee population never missed the additional frames removed, and will help mitigate swarming by removing bees and keeping brood nest open.
I started a NUC MAY 17 and they they have drawn and half filled third deep so I'll get at least a super of honey.
Thriving hive is still going like gang busters( now five deeps and bearding on 90F days) so I started another NUC and just removed three frames of capped brood to add to another NUC. This opens up the brood and nurse bees need to drawn comb. Have extracted 35 lbs of honey as well and I can give them wet/open comb to fill again.
Keep the strong hive thriving and producing honey and build up NUCs/additional hives on the side be removing a few frames.
If you always do what you always did, you'll always get what you always got!