The honey has crystallized. Can I just weigh it out into the fermenter, add the apple juice, and figure it'll dissolve and mix up eventually? Or do I have to liquify and then mix?
You *can* just add it in and the yeast will eventually get to all of it. I would heat it some so make it a bit easier to work with and mix it in to dissolve as much as you can reasonable get it to. I don't know if it affects it at all, but you can lightly heat it in the microwave to speed it up before mixing into your juice.
Should I oxygenate the must? I have a tank and a wand.
Oxygenate it. It will only help your yeast colony when getting started and you already have an easy method to do it.
I'm musing about whether to replace 1 of the gallons of AJ with RO water, to move it a bit from cider towards mead (and so the apple doesn't overpower the honey.) Does this sound like a good idea or not?
This is strictly a style choice. I'd go the full juice route and see how you like it. You can always do another batch where you water it down.
For the oak addition, I'm thinking about soaking it in dark rum for ~2 days, then adding both oak and rum to the fermenter when I think I'm a week or two out from bottling. Should I also add a dollop more honey at this point to restart fermentation and try to limit oxidation? Does this sound like the right amount of oak? Is the rum going to be too strong? How does the timing sound?
I can't really help with the rum aspect as I haven't done what you are asking. My rum experience is using a barrel that previously held rum; that is with pyments and not cysers. What I can suggest is that you might add the oak up front in primary and let it start its work right away. I would go with 1g per liter. You don't say what your final volume is but your recipe says 2 gallon apple juice and 5Lb. honey. That will give us a volume just under 2.5 gallons... that would be ~9.5g of oak in primary.
I don't really have a suitable secondary fermenter. Can I skip secondary, ferment until dry in primary
You don't have to transfer to a secondary vessel, but it certainly makes it easier to have a clear mead when you go to bottle as you aren't trying to avoid the large sediment at the bottom.
The next item to be careful of is how long you leave it on the gross lees (sediment, fermentation crap) as that can affect the flavor of what you are making. This is where transferring to secondary make a lot of sense.
then transfer with priming sugar into EZ-Caps? Or should I prime with honey?
Looking at your recipe you have 2 gallons of honey and 5Lb of honey. 6 Lb. of honey is ~ 1/2 gallon. I'll guess your final volume is 2.5 gallons of must, as you didn't list water and you questioned swapping some juice out for water.
You will be looking at an OG of ~1.125 which has the potential to take you all the way to 16% ABV. D47 tops out around 15%. If the yeast stops at 15% you will have ~1.010 SG left to give you some sweetness. You will not have to worry about priming sugar as there will not be any ability of the yeast to eat it and provide carbonation.
As you mentioned priming sugar or using honey to prime, you will need to have some yeast there that can actually still ferment to produce that carbonation... this means dropping that high OG to something lower that will finish dry and still have some life left to ferment your priming sugar.
The easiest method would be to add some water to bring your final volume up to 3 gallons, which would make your OG ~1.105 obtaining an ABV of ~13.5%. D47 will take that dry and should still have the ability to make use of priming sugar.
IMO, I try to keep things like this in the realm of 10-12% ABV. I use less materials, the ferment is done sooner, and I have less wait time for everything to blend and be ready.
