Geo Search API for Travel Network (Backend Rebuild / AI? ML?)

I have a travel app, that stores posts around the world. I need you to rebuild the backend, as I want to move away from firebase.

App Overview:
- Users post sights, tips, tricks etc at locations (user, time, coordinates, text, images, tags)
- Users vote posts (post, time, up/down)

Backend Requirements:
- Intelligent indexing of posts based on location, tags and votes
- Intelligent indexing of users based on what they have voted
- Querying user relevant posts around his location
- Full text search of posts around a location (preferably also user relevant)

Nice to have:
- Adjustment of timeframe to include/exclude votes (e.g. results relevant this month)
- Ideas/Possibilities to integrate Machine Learning

Obviously performance and low pricing is key. Please let me know if this is something you can help me with, looking forward to work together!