Advice on IP

I'm 20, going to finish university next year and will be earning around 47 000 for my graduate year before tax. I already got a property this year that's in neutral gearing atm (hopefully positive once rent goes up). It's a P & I loan and i don't have to worry about it because the rent covers the repayment and my parents sometimes pay extra on it (Its more like my parent's house with my name on it).  However I'm interested in getting my own IP with my own money. By the end of next year I will have around $35 000 as a deposit. I was hoping to get a house around $300 000, IO loan. It will calculated so that the rent will pay for the repayment, and i'll set up a 100% offset account. I can probably save around $20 000 a year which will be in my offset account. That's where i'm lost. I know the steps into getting the first Investment property, but i don't understand how people on low salary is able to buy a house every 6 months, because i didn't think 6 months is long enough time to accumulate equity in your first house. My question is am I planning it right? My goal is probably buy an investment house every two years relying only on my money. I will of couse live at home so it's a lot easier to save, and it's possible to ask my dad to deposit around $50 000 in my offset account until he needs it, therefore more cash flow for me. It's the next step, after two years house prices is probably up, will my savings of $40 000 be enough to invest in another house? Also with IO, i understand that by having an offset account its pretty much like P&I, but when i used the money in the offset for investment, that means i had paid nothing into the principle for the first home and it goes on to the second, third house etc. How do people in the end ended up with 10 properties when they paid no principle, and get to live the life. My goal is able to live off my investment by the time I'm 35 (is that realistic?). Its the accumulating debts that I'm worried about, don't want  to go bankrupt.