How many colleges should I apply to?
It depends on how much work you want to put in, how balanced your list is (reaches vs safeties) and how much money you have to spend on app fees, unless you have waivers. Many high schools suggest around 6-10. On this board, where things are skewed towards more selective schools and some very selective schools, you will see people applying to many more than that.
What’s more important than how many schools to apply to is if your list contains schools that you can get into, and can afford.
My daughter has a close friend who applied to one school: accepted in September to a rolling-admissions school that she loved, and was done. Very happy, no regrets, and was able to enjoy her senior year while the rest of her friends freaked out about college apps. At the other extreme, they also had friends who applied to 20+ schools.
It all depends. You need at least one school that you know you can get into and afford, where you’d be happy to attend. Beyond that, it depends how many “lottery tickets” you want to buy for schools that are reaches, and/or schools that are matches/safeties but offer competitive merit scholarships that you may or may not get. It also depends on whether you’re clear on what you want (major-wise, location-wise, and so on for various other attributes) or whether you want to apply to several different types of programs and decide later which direction to go in.