I just speak out of outer scope:
It's not a problem to hire someone. It's a problem for ROI and how fast the investment can be earned back.
If the calculations and assumptions are solid, why not?
In my experience, it's difficult to write a good catalog of needings. Most of the time this and that isn't thought about and will lead to problems later, making the whole thing slow developed and costly.
So, if you have a good thoroughly thought plan, why not hire an agency? Also, it should be somewhere where you can walk to. May be the same city. Conversation with the developers is the most important part in such things. If they're in India and you're us based - then for sure you won't really get what you want.
Also, if you want to keep your costs low later, the programming should happen with cost optimization in mind. I don't think it's possible to get that from an agency, which focuses to develop in shortest time. Then you'll get a behemoth of code with big dev debt.
What about searching for a companion with same mindset and do the programming together? It's better than doing everything alone.. and may be introducing some dev debt because of no discussions on problem solving and approaching?
Wish you the best and much more success with your project!