Ehh madman don't have a .. like universal term, so it's hard to say what is allowed and whatnot. Usually lowering the dismember threshold is looked down upon.
You can change the gravity I guess, the common ones are default and 0.00 0.00 -30.00 (sambo gravity), but for madmans people usually just leave it default.
To be honest madman isn't really an accomplishment anymore, you can create much better replays with a single target like decap, or something completely different. But if you do want a madman, make it stylish, make it original, quality matters and not quantity so hugging uke off into 20 pieces isn't anything worth watching, clear and nice hits are what people like to watch. Speed is always good : )
Replays may seem to have easy dismembers because they have tens and tens of edits in them, where people carefully edit each hit to be a successful one. There's much more to a beautiful replay than you might see when watching it. I'll leave tips about how to dismember to someone else, my text is probably getting too confusing from lack of sleep.
Yeah, poses usually are a way of ending your replay, if you're still a beginner, try laying down in some way so you can balance yourself, more experienced people sometimes just try standing up on two legs and get a pose, but that's quite advanced.