I need help with a project

Hi everyone! I'm a beginner and I want to master Rust. The company I work for needs an app to streamline/automate processes, so I'd like to submit a proposal and practice my Rust skills (learning by doing). Here are the details:

Extract data from CSV, .xls, and .xlsx files, save it to a database, and send/export the data to Excel, CSV, and via a Telegram bot (raw data -> processed data).

Other requirements:

A collaborative tool (desktop app). Everyone can use the app offline, make changes, and those changes are merged when connecting to a LAN.

Challenges:

The company isn't focused on software development; there's no server or anything like that, and they can't afford it because they don't have any developers. This is just a proposal I wanted to share.

The only "available" computer will be my MacBook Air M4 with 16GB of RAM, but I clearly use it for my daily work, specifically for development, so its resources are limited.

This tool will be for my colleagues; they aren't technical, so it needs to be as simple and easy as possible for them.

The data importers will be 2-8 users, and the data viewers will be between 10 and 30 users (via Telegram). The amount of data is, let's say, 1 million annually (slightly less) over 5 years, totaling 5 million data points that need to be stored and managed by the 2-8 users handling the information.

I know what to use for the obvious tasks: Calamine for reading Excel files, Teloxide for the Telegram bot, etc.

What I'm not clear on and need help with is which database to use? Fusion system, server? Peer-to-peer? CDRT 'parrot'? Basically, I'm lost when it comes to connecting and merging data and how to save it.