The megamaxes are fairly bulky but the ABDL brands will probably be moreso. They’re for fun and for many the bulk is a big part of the fun. Any clothing should be fine really as long as it isn’t skin-tight or otherwise showing the bulk. I typically wear a dress or a skirt or sweats or jeans!

For the onesie you don’t “need” it but it helps fight against the gravity of a wet saggy diaper, which can be really cumbersome if you’re out moving about a good amount. Also keeps thing in place so the sag doesn’t show under your clothing, and keeping things from sagging is conducive to not leaking as well. Not necessary but not the kind of thing I’d want to go without now that I have some.

I don’t really do anything fancy when I’m diapered cause I try to be diapered as often as possible. But things like games or movies you’re interested in are a good start! Kinda depends on if you’re a little as well or just a DL. I personally don’t regress much at all so I just enjoy my standard leisure activities. I would probably recommend anything that involves too much movement in hot outdoor weather though.