A few questions about dry-hopping the keg

Do alpha-acids matter? Since this is just for aroma, I would think it matters less? I have some Centennial leaf hops that are a little low on the AA report for the varietal at 8.8 AA.

Are pellets or leaf/whole hops better and why?

How long should they stay in contact with the beer? Should I let the beer carbonate before dropping them in?

ive used both and i get better flavor from whole leaf hops however they soak up more beer I have never hopped IN the keg, only in secondary for between 6-10 days depending on the recipe and then i will keg after

If you listen to the BrewStrong podcast Jamil has done a dry hop episode. First it totally depends on the style. From listening to them the general consensus is they use pellets and from what John Palmer was saying the higher the AA is kinda a indicator of the oils and thats what you really want. so the higher the AA is also the less you have to let them sit. Generally you let them sit for a week but it needs to be tested often. if what your looking for happens after only 2 days there ya go.

Looking at the USDA information, oil % varies more than AA and it is reasonable to think that the same conditions that increase AA% would increase oil production.

USDA info for Chinook:
ALPHA ACIDS: 13.6 (5 year average: 13.9-15.3%)
OIL: 1.83 ml/100 g (5-year range 1.24 to 2.63)

Whole hops are less of a pain to work with. Pellet hops will shed bits regardless of how fine a mesh you bag has.

1-2 weeks

Do not carbonate first. If you carbonate & use pellets, plan on a foam-out.