Character, Selecting Effects, Scripting, Presentation .... am I missing anything?
Practicing? I remember you writing in a thread about that somewhere, let me see if I have that bookmarked in another browser...
Nope, doesn't seem like it. But I remember that you shared some valuable approaches on how to go about practicing your set, insights that may bear repeating in your workshop.
Apart from that, how about "post-production"? Marketing, how to find an appropriate venue, get booked, get paid etc.
Are there any good books or resources on building magic acts?
Read
this fantastic thread created by @WithDocIsIn. He details his process of creating a show from the very beginning and discusses different approaches with other knowledgable magicians on the forum. It's not a "how to" on building a magic act, but will give you invaluable insight into the mind of a professional performer of magic and mentalism.