1.) Your Up+B is so laggy that your opponent can give a nice WD or SpotDodge and figure out what to do with you. So I would so no. WDing out of your shield or beginning a shffl I would say is a better option, seeing as WD gives you an opp to start being a projectile prostitute, and shffling gives nice quick damage. You might get your opponent with this ONCE maybe, but it only does a small amount anyway(Can't think of exact off my haead)
2.) I would say no to this as well. The Flame Spike is not an incredibly useful attack to begin with, not to mention takes alot of practice for something you can do with a D-Tilt. Sure it's flashier, but people may view you as a prick if you intentionally do it all the time. People usually do it on accident.
3.) If Peach is coming horizantally, shes gonna make it back, so I would suggest Rang and Bombs for stun, then a nice Boot the her face. If she's coming from below the stage, you could try to Spike her, and use a D-Smash, which is a little safer.