Now that you've hired a developer and you're ready to build your MVP, I want to re-iterate that this should be a throw-away MVP.
Make it very clear to your developer that what they're building is a throw-away codebase.
Don't allow them to waste time thinking about problems at scale. You don't have scale yet and may never have scale with the product as you imagine it today.
And you don't need to automate everything yet.
At this phase, fall in love with the concept of "Being the Software".
By "Be the Software", I mean you don't need to spend a bunch of money building out complex backends to automate processes.
If you need to manually send confirmation emails to every new sign up, do it.
If you need to manually play the role of an algorithm behind the scenes and manually add recommendations to customer accounts, do it.
Ultimately, you don't know what's going to stick. So don't build complex software if you don't need to. Be the software.
Remember that this a learning experience.
Your goal as you build this MVP is to build things as quickly as possible so your customers can test things as quickly as possible.
Build things that feel unfinished and get the users on your waitlist to test them out.
If users can test it, it's finished enough.
You can't chase perfection at this step.
Your goal here is to learn what works and what doesn't.
As you build more features, feel free to invite more users to test your MVP.
Just make sure they know it's an MVP and that they're early adopters. Don't "fake it until you make it". I hate that phrase.
Also I'm going to recommend it again if you haven't read it yet. Read The Lean Startup.
And I'll also include a couple other resources that should be helpful.
But you're officially in-motion. If you don't have mentors yet for whatever reason, definitely find some.
They'll be a lot of help here.
This is where you get into all the "extra" stuff you need to do to pursue your idea.
You're officially taking flight.
Stay in flight until you have a version of your MVP that customers are actually using.
You're done when you're not relying on your own optimism about this idea to keep moving forward, and are also relying on feedback from your customers.
When customer feedback and behavior validates your idea, you're ready to move on.