The best answer to this is to think very very very carefully about if you want to invest in doing things properly.
Short of pointing you to LMS themes https://themeforest.net/category/wordpress?term=lms#content, and generic credits/contest (will almost certainly not be set up for coding challenges etc - which would take a dedicated tool/app) plugins then it’s pretty much impossible to answer because it’s just not that simple…
Simply by finding a hacked solution that relies on multiple plugins creates immediate concerns/considerations around:
- compatibility between theme and different plugins
- consistency in terms of front end visual and even more importantly back end data management
- what happens when updates happen? This could easily then require/rely on changes from multiple different authors or sources.
More than anything - you will be handling super-sensitive data which will mean serious (financial, technical, maintenance) investment (on an ongoing basis) in proper hosting and security (not to mention legal protection), all of which is not made any easier with a mix of different solutions involved, and will further influence choice of theme/plugins
We’re not trying to dampen your enthusiasm - just make sure you have a realistic view of what is (done properly) a complex job.
If you want to do this then you will save yourself a great deal of time, stress and budget long term by investing in creating a custom solution for your purpose through a developer/agency who can support it, so that you don’t find yourself with an unusable website/platform after the first update.