Well you don't really have to secondary so might as well do it in the primary... Wait until the krausen has disappeared and then add the hops. Let them in for 5 to 8 days before bottling. Do transfer to a bottling bucket for bottling (dryhop or not, never bottle directly from the primary).
I tend to sterilize a mesh bag by vapour cooking it for 10 minutes and then add the hops, tie a knot and pitch it in the fermenter. Could also use sanitizer... (but never sterilize/sanitize the hops).
A lot of people just throw the hops in there and you might as well do that... I really prefer leaf hops for dryhop. Almost any flavourish american hop will be great for an IPA. Cascade, Amarillo, Citra, Centennial, Simcoe, Willamette... In 5 gallons I'd throw at least 2 onces but even 1 will have an effect...
Dryhopping is like pitching flowers aromas in your beer....
Oh I almost forgot to wink! ;-)
