You want to buy a house for $150,000. It may be possible to do this with $10,000 and a 3.5% downpayment, but it would be a lot better to have $40,000 and make a 20% downpayment. That would give you a cushion in case house prices fall, and there are often advantages to a 20% downpayment (lower rate; less mandatory insurance).
You have an income of $35,000 and expenses of $23,000 (if you are careful with the money--what if you aren't?). You should have savings of either $17,500 or $11,500 in case of emergencies. Perhaps you simply weren't mentioning that. Note that you also need at least $137 * 26 = $3562 more to cover mortgage payments, so $15,062 by the expenses standard. This is in addition to the $40,000 for downpayment and closing costs.
What do you plan to do if there is a problem with the new house, e.g. you need a new roof? Or smaller expenses like a new furnace or appliance? A plumbing problem? Damages from a storm? What if the tenants' teenage child has a party and trashes the place? What if your tenants stop paying rent but refuse to move out, trashing the place while being evicted? Your emergency savings need to be able to cover those situations.
You checked comps (comparable properties). Great! But notice that you are looking at a one bathroom property for $150,000 and comparing to $180,000 houses. Consider that you may not get the $235 for that house, which is cheaper. Perhaps the rent for that house will only be $195 or less, because one bathroom doesn't really support three bedrooms of people.
While real estate can be part of a portfolio, balance would suggest that much more of your portfolio be in things like stocks and bonds. What are you doing for retirement? Are you maxing out any tax-advantaged options that you have available? It might be better to do that before entering the real estate market.
I am a 23 year old Australian man with a degree in computer science and a steady job from home working as a web developer.
I'm a bit unclear on this. What makes the job steady? Is it employment with a large company? Are you self-employed with what has been a steady flow of customers? Regardless of which it is, consider the possibility of a recession. The company can lay you off (presumably you are at the bottom of the seniority). The new customers may be reluctant to start new projects while their cash flow is restrained. And your tenants may move out. At the same time. What will you do then?
A mortgage is an obligation. You have to pay it regardless. While currently flush, are you the kind of flush that can weather a major setback? I would feel a lot better about an investment like this if you had $600,000 in savings and were using this as a complementary investment to broaden your portfolio. Even if you had $60,000 in savings and would still have substantial savings after the purchase. This feels more like you are trying to maximize your purchase. Money burning a hole in your pocket and trying to escape.
It would be a lot safer to stick to securities. The worst that happens there is that you lose your investment (and it's more likely that the value will be reduced but recover). With mortgages, you can lose your entire investment and then some. Yes, the price may recover, but it may do so after the bank forecloses on the mortgage.