First of all, don't be afraid to share and exposing your business model. The Fear of stealing ideas is limiting you.
I don't know your business model, your idea, your service or product, but no one of these will be the key of your success.
The people, and how you talk to your market, will be.
You don't sell product or service, you sell yourself (people) ... especially in the first time of your startup, when no one knows you.
Every day someone builds a product or service that is a copy of another. The difference is the market and how he/she talks to the market.
Back to your question.
Hire one senior, skilled person, that after will be in charge of hiring other people is a right way.
I didn't understand the reasons of why outsourcing wasn't the right way to follow. Costs? Was it a firm?
Don't know. But...
I can share a simple process that I follow every time in my business, even if I'm a developer and I could write all the code, I didn't write a line of code for software that serves my clients.
You have to sketch your solution (application).
Do it with tools or pen and paper (the right tool is better).
I use keynote for mac or balsamiq is also a great tool.
You have to have the entire application designed. Every page, every feature is running in the sketch. All the elements.
It'll take a lot of hours or even days.
Don't care about design and "looks good" now. Be fast.
Don't care about "is it possible this?" question. Sketch it and write a note or doubts in a post-it.
Now you don't have only a clear vision in you mind, you also have something that you can share with a developers.
Developers are strage guys.
They can build and make things from nothing but it's not easy when the product is placed only in a corner of your mind.
"Rock Star" developers loves to work on UI (user interfaces). There is no-way to get off the road.
And when they perfectly understand your application, they can give you advice, clear your doubts and build it faster.
The key point here is to get the version 1.0 as fast as you can. Give it to your market and get feedback.
To overcame the fear of stealing ideas, you could split your big application in a lot of smaller pieces.
You should search and hire rock star freelances from website like upwork.com and give to a single professional only a small task.
Then, hire a trusted person that put all together, like a puzzle. This works, I know a few friends that do this strategy.
I can't tell you more than this, because a lot of decision depends of what are you trying to build, how much money you can invest and what are getting you stuck.