Seeking advise for investment property and offset account

Hi, Here is my situation. I bought an apartment in 2008 which cost me approx 170K.It is worth of 210K now. I took home loan amount of approx 115K from bank when I bought. I did not have an offset account setup at that time. It was just normal home loan account. Property was rented out for approx 7 months, and then I moved there and have been living there since then. Gradually, I have repaid/deposited on my loan account approx 85K extra already beside my regular monthly payment for home loan so that I get less interest from bank. This 85K I can take out anytime if required that is how home loan account was set up with variable interest rate. Note this was not an offset account. I have only 15K left now to repay my full loan. Now, I am planning to make this as an investment property and buy a new house and would like to take out that 85K what I have already paid extra, what I can use to buy new house where I am planning to live. This will result the remaining 100K as Loan in my investment property what will be rented out and planning to make that as an interest only loan account. My question is, as it was not an offset account but still I can take out that 85K, and will I be able to claim tax benefit on 100K if I rented out this property or I can only claim 15K(100K-85K) on tax benefit. If I don’t get tax benefit from 100K, rather only on 15K, I may think on different options. I will appreciate for any feedback Thanks Investment property seeker