I don't know anything about illusions or bizarre magic. Rick Maue published a popular book on bizarre magic, so you may find some help there.
However, re. mentalism: my array of mentalism tricks gelled into a full 45-minute act in 2003, so I can give you the point of view from having recently constructed it.
With mentalism, you first have to decide on an approach. Do you present yourself as real? Are you ambiguous in proclaiming what you do? What premise do you give the audience up front? My premise consists of just two sentences up front. You can perform an act without such a proclamation, but I believe that audiences want something to grasp onto in mentalism.
Once you have that nailed down, you'll find that a few things fall into place.
Finding some logical order to the trix is important. Finding a knockout final trick--something that's totally reliable to knock audiences out--is essential. And a good, quick first effect is important, too.
Once the order of tricks is chosen, the mature show starts interweaving the tricks with callbacks and interactions between the tricks. Also, the best shows have a through line, a kind of plot that makes the audience have to watch until the very end. It's different in every show, of course.
Figuring out music can be difficult, esp if you don't have a music tech at each show that you do. Music should enhance, never dominate.
Finding a place to practice your show is the toughest thing. There are things you can learn about a show only by performing it in venues where you don't have to be great.