People matter, you need to be communicating to keep communicating up, not get stuck repeating yourself and losing your soul. It keeps accountability up.
You need diversity in your team, even though that has costs and friction. You need experienced older people, not because of some advantage (there are some, but if young, you probably won't see it), but because younger people, graduates on a student salary, will want to naturally explore, move city with their boyfriend, move on - unfortunately if you train up someone for two years, it's normal that they won't become an early product lead, they will actually leave. Yes maybe you can pay enough for a startup but - experienced people are more likely to stay, and work much better. 1 bad staff member counters 2-3 good ones. At start up level, that's life or death. Try and get HR and management experience (particularly with high churn) before startup so you learn people-HR skills and understand this dynamic, so that you don't kill your startup for someone else extracting from you/your kindness
Secondly, try and do things with 2 magnitudes higher amounts of potential success than you need. Avoid things where you think you can make 10k or even 50k a month - the minimum viable needs to 250k, for part of the market. Otherwise, you'll plateau on either growth, certain marketing channels, employing in the niche - those don't make sense for a sole purpose startup.
Have budget ahead to cover things but set deadlines. If possible, try doing a side hustle/startup with a part time staff member filing corporation taxes 1-2 years ahead. You'll learn the ropes of stuff that will save you valuable time when you need to crush taxes.
Don't let yourself go into CC debt for a company... classic student mistake. generally every $ of credit will take $$ to get out of for a college grad (not just in terms of numbers - you will feel less confident in debt, it'll cost you in other areas of life. Like your partner breaking up with you). Don't listen to peoples advice if it's too general, go for specific advice.
If your results and your self-view is that you are in the top 10% of something and you have received compliments, never take advice on that thing. You'll be told things that apply to the bottom 70% and could make your performance worse... lean on those strengths.
be ready for friends to leave, abandon, disbelieve you, hate that you work late, and don't recognize that they doubted you when you do succeed. Same for partners. Unfortunately, a lot of startup founders start single, and a different group end up single. Doing a startup is a major change for a partnership so consider that before you make the step.