Well, I uploaded part 5 of my story, which is the final part.
There are pros and cons to the various approaches you can take. If you are planning on using established characters then you need to try and get those characters clear in your head and decide how you want to use them. I find it helps to imagine the actors delivering the lines in my head to try and make the dialogue sound like the character but whether other people are getting the right vibe is entirely personal to them.
If you ask for ideas from others, are you just going to script their plot ideas or ask for full scripts with dialogue intact - it might be tougher to realise somebody else's vision.
My basic premise was that I wanted to explore the interactions in a Trek world featuring the key, interesting races from other sci fi genres.
I'm not a huge fan of the overly sterile form of Trek so I wanted to make the world of the Federation a little bit murkier, building on concepts from the novel Traitor Winds, Star Trek VI, and Babylon 5.
I wanted to go for a more a diverse crew so I picked Star Trek the Motion Picture, which featured many different species and an awesome series of Enterprise sets.
I also wanted to go for more of an ensemble vibe because I'm not a fan of placing full focus on Kirk, Spock, and McCoy where other characters feel more appropriate (once again, this vibe came from Traitor Winds). Although she was relegated to cameos in TOS, I have always been a fan of Yeoman Rand and I was surprised at how easy it was to flesh out her character using elements gleaned from the show. I was also pleasantly surprised at how people enjoyed her little jaunt with Berruzha (channelling just a tiny bit of Sigourney Weaver but I stopped short of a scene in her pants).
My mistake (apart from being cheesy) was starting with only a vague plot and then building the story around that because I allowed the proliferation of too many characters. I found that it wasn't possible for different characters to know key plot points that the audience know, which necessitates repetition. I also underestimated how much technobabble can bog you down in comic book format where dialogue should be fairly light.
I think you should start with your own plot ideas, see how much you enjoy writing and producing the stories, and then go with the flow.
