Releasing equity

Hi there.

This is my first post on this forum & have interest in releasing equity to purchase an investment property. I have basic knowledge of how equity works, but just got a couple of questions if people would be keen to help a little!

My house currently would be valued around $485k. I have $285k left over on my mortgage. So that would equate to $200k in equity, and with the 80% I can utilise that makes it $103k of available equity? Of that 103k I can use it for a deposit, stamp duty and other fees?

Say I then have 50k left of that available equity am I able to access that to pay towards the investment property repayments if I can’t out of my current cash flow?

Also I assume I pay interest on the equity borrowed, how does that work, does it come out of my pocket?

I have a general understanding of how much equity I will have available, just not sure exactly on how I can use it and what it will cost to use it also.

Would appreciate any help.

Thanks,
Fudge93842