Mobile App Compatible for Android and Apple Devices

I'm looking for mobile app developer to build a cross platform application for Android and iOS devices.

It will be an app where people rate each other over an event* (Event will be notify in a later stage when project is awarded). The criteria of rating will be given as well.

I don't need it to have a lot of features, The key things I would need is.

1. Ability for people to create a free account/login through Social Media or Email (Simple Signup/Login Form).
2. Each user of the app will have unique QR Code when signup/register for account.
3. Simple options to find "Events"
4. Each user who performing the "event" shall get connected thru QR Code to enjoy rating each other.
5. User able to tag Location of the "event" take place.
6. Option to chat with another user.
7. Option to review another user ratings.

At this point of time, this is just an idea. We will discuss further once I find the right fit.

Kindly please provide the following:
1. Estimate timeline and cost
2. Send me portfolio
3. Propose a development language

Thank you.