ETN(CryptoNight) - Median block size, block time, block reward

Hi, i know some basic stuff how btc work.. I mean how diff changing block time etc...

But cryptonight is liiiitle bit different... I wanna ask someone who know mroe about it to explain me some stuff...

1.What changing median block size?
2.What changing block time ? Sometimes is 14sec.. sometimes 30 min...
3.Why are some blocks empty? For example right now.. 26/02/2018-11:00 CET... In transaction pool is 870 transaction with 7500kb size... but when i check last blocks.. sometimes pools will find blocks witch 0 transactions.
4.I find somewhere if block size is bigger than median reward is little bit lower, is that true ?
5. What changing block reward ?

If someone will find time to explain me this... If he will show some mathematics example... I will honor you.

Thank you