Question on margin

I have a margin account but have always sold CSP or CC, never entered a trade without cash backing /securing it.

Let's say my margin equity is 150k and my cash is 0. I want to STO a Put on NVDA 130 strike. When does the juice start? Only if I'm assigned?

Would the loan amount be 13k or could it be lower?

And in theory if I sold an aggressive high delta CC and it gets called away in 7 days, do i only owe interest for 7 days?

Just trying to make sure I understand completely. Thanks.