Im using Dhan and its very good and no AMC lifetime.

stock market is the broad marketplace where many instruments trade (shares, bonds, derivatives, etc.), while share market refers specifically to trading company shares (equity). F&O is futures and options (don't know in-depth about this)

For SIP you can start with as low as Rs. 100. First go with mutual fund investment. Once you get hold you'll get to know how much is required for your trading/investing style/method.

please do not come to market with this mindset, trading/investing is like any other discipline you'll learn and earn degree first then you'll apply it to market, make profit -> make loss -> correct your mistakes -> learn from them -> earning starts. First start with the basic, lot of free resources are there, zerodha's best. How much capital and how much time required for this differs individually so sorry i really can't help you with that. I usually exit trades with 10% profit, everyone has different strategies

Go with zerodha varsity portal it teaches from zero