If you are a great engineer that can get a job at FAAG, joining a start up is almost never worth it from a strictly financial point of view.
17 years ago, Paul Graham was able to post this essay: http://www.paulgraham.com/wealth.html - nowadays, the compensation in tech has shifted upwards so much (https://www.levels.fyi/) - that start ups are just not competitive when you adjust for a risk premium. Finance captures this concept using metrics such as the Sharpe ratio (https://en.wikipedia.org/wiki/Sharpe_ratio) - which measures how much extra returns you are getting in exchange for the additional risk you take on. For start ups - your expected returns are lower, and the risk is very significantly higher.
Are there other great reasons to join start ups? Absolutely: several start ups are working on exceptionally cool science problems, some are solving tasks that will make a meaningful improvement in the lives of people (https://detroitwaterproject.org/, etc), some people just prefer working in a small company, you get a chance to work with your friends - but - if you are going to work for a generic SAAS company, don't accept a pay cut.
The VC that's financing your start up evaluates their investments with a spreadsheet and zero affection. Ask them how they sacrifice their own income to work on more interesting work, and they'll (politely) laugh in your face.
The killer feature of Nim is its amazing syntax. If you know Python, Nim will instantly feel very, very familiar.
Rust looks incredibly useful to do systems level programming, and guaranteed pointer safety without GC costs is amazing, but it takes me much longer to figure out exactly what's happening in the code.