Unless the mead is SUPER clear already, leave it in bulk. Most of us will age until it's reached that level of clarity so that we don't get a metric ass-ton of sediment in the bottles.
I go a minimum of a year from mixing to bottling for my low ABV meads (for me, that's 14% and under).
I have developed my own guidelines for aging mead.
<14%, plan on a year from mix to bottling.
14-16%, plan on 12-14 months mix to bottling.
16-18%, plan on 14-18 months mix to bottling.
18-21%, plan on 18-24 months mix to bottling.
21%>, plan at least two years.
These are the guidelines that I've found to work really, really well at least with traditional meads, and the melomel I've made so far.
As for what to use for the vessel, it really depends. More recent postings/threads have indicated that a quality PET/HDPE carboy is 'safe' for use for extended aging. Since you'll probably be racking it every few months (2-4 is normal), look at it that way. Personally, I just use sanke kegs that I've adapted for fermenting in.
Something else to keep in mind. Once you bottle the batch, you're done with any changes/tweakings/etc. So, if you try some later and think "damn, this could have been oak aged", guess what... Too late.
If you leave it in bulk, you can put it on oak for a while and then take it off. You can do a lot more with it too. IMO, 10000 times better off just letting the batch age in bulk form.
As for the head space in the vessel... IF it's one you can seal up right, you can use CO2 there. Plenty of sources you can use to get the CO2 into it. If you're looking to keg, you can use a corny keg, fill it with the mead (to age) and purge the head space as normal. Just be sure to vent out the CO2 pressure (once the lid is sealed) so that you don't carbonate it.
Unless you WANT a carbonated mead that is.