Questions about ESC 4 in 1 and flight controller

I’m currently watching tutorials about building a custom drone, but I have some questions that YouTube videos haven’t answered clearly.1.) Is a 4 in 1 better than getting 4 individual ESC?2.) What does it mean when 4 in 1 has various numbers such as 16x16 or 20x20 or 30x30 ?3.) Any suggestions on what are some good ESC (preferably 4 in 1)? The market is rather saturated, and I don’t know so much about them.4.) Are ESC universal to flight controllers, or do I need specific specs to the corresponding flight controller?5,) I would also like some recommendations for a flight controller. I’m currently looking at a Mamba F722S because of a YouTuber. Same goes for a transmitter, many seem to recommend FrSky brands. via /r/drones https://ift.tt/3187VAl