Whether or not to use a secondary is totally a matter of personal preference. I choose to do most of my brews with just a primary. Unless I'm adding something extra for secondary fermentation, I don't bother with a secondary. I see it as necessary risk vs. unnecessary risk... Transferring to bottling bucket is a necessary step to add priming sugar and get my beer into bottles. Transferring to secondary is an unnecessary risk because autolysis isn't an issue I've ever encountered and it opens my beer up to potential for oxidation. Some people think that secondary really helps with clearing. I happen to think that conditioning (primary and bottle) will yield similar or equivalent results most times.
Dry hopping an IPA? DEFINITELY
I toss 'em right into the primary. No bag. The pellets settle out into the trub just fine.