How often do channels stay open for a long time? When they are closed then a fee is created for the miner right?

I remember hearing you can keep channel open but sell some of the bitcoin back onto main chain so fee created in the process. ?? Not sure if that's right.

So seems like could keep a channel open indefinitely trading bitcoin via lightning. Then no fees for miners. So this applies to smaller transactions below $1000.

Bigger transactions above $1000 will be done on chain. So fees from bigger are considerable. 

As price of Bitcoin goes up, then threshold for doing transaction on lightning will go higher because fees for onchsin goes up. 

So are you saying in the future people will be transacting eg. $10,000 transactions on lightning. Per transaction for example?

Just thinking it through in my head.

I haven't learned lightning properly, just heard its really good, instantaneous transactions, next to no fees for really small transactions etc.