display – MacBook Pro 16 2019 + External Monitor. Battery Life

I’ve recently bought a MBP Pro 16′ 2019. I’m using right now a Thunderbolt 2 adapter so I can connect it to an old iMac 21′ and using as an external monitor.

My question is: It is safe for battery life keep it connected all the time?

Right now, I’m only working from Home (Pandemic) and I’m afraid of leaving it at power source all the time.

I don’t mind when it hits 80% of battery charge, unplug and plug again when it’s 30%. But just to clarify if it’s correct.

Also, I’m planning on buying an LG Monitor with Thunderbolt 3, that has an 85W plug connector to provide energy to the MBP. Should I use it? The official charger is 96W.

Well, thanks for your answers.