This is bad advice, IMO. Most (non Star Trek) publishers, in my experience, want to know the book is completely written. The outline is only there to let them know the story hangs together, the first three chapters tell them your writing ability. ... Unless you are the most gifted, brilliant writer on Earth, every manuscript goes through multiple revisions to get it into acceptable shape.
I'm in the process of writing an original spec novel, and I'm diverging hugely from my outline. The outline I have now is just a rough guide for myself. Once I get the manuscript finished and refined, I'm going to need to write a whole new outline/synopsis for the benefit of agents and publishers, one that accurately reflects the finished story.
That's not the way it works in tie-ins, as Dayton says. The studio has to approve your story outline before you write the book, and it's expected that you'll conform fairly closely to what you submitted.
If you want to be a novelist and insist on breaking in with a Trek book, write it from beginning to end. Then re-write it. Then have someone who knows writing look at it and give feedback (you may have to pay someone for this - be careful and do research before handing over any money). Then rewrite it again.
Actually it's best to do that with a non-Trek book. If you're pitching to Trek through the submission process, the outline and sample chapters are all you should write -- particularly since it's likely to be just a "demo" of your skills and may not actually get purchased at all. The point of the Trek submission process is to sell yourself, to prove your ability as a writer and your ability to follow instructions. There's no point in putting all that effort into a full manuscript that may never be sold. Sure, it's valuable for getting practice and experience, but in that case it's better to get your practice with original fiction, because then you might actually be able to market it.
And paying someone to read your work? I'm skeptical that that's a good idea. Generally you should beware of anyone asking you to pay them for help with your writing. Beta readers should be people you trust to give you an honest reaction. People who are trying to get money from you generally don't fall into that category.