Absolutely nothing about this is any simple. WordPress was never engineered to smoothly integrate with other systems. Though that is quite commonly done in practice.
You have multiple distinct challenges here that all need to be studied, scoped, and developed:
- What data needs to be saved in WP installation and which data structures are appropriate for it
- Does the two system need to share authentication and if so how, which of them is canonical and how cross–login will be implemented
- Is the data completely separate between the system, or there needs to be degree of sharing/accessing/moving between the two
While I do think this can be cobbled together from some off-the-shelf pieces (maybe halfway), I do not think that is a genuinely good idea for someone new to WP to attempt.
If you are set on doing this I would recommend to start breaking this down in more specific challenges to ask questions about. 🙂