One more inaccuracy

Your calculation uses average annual rate of return (~4%). However, in different period, actual rate of return can be very different. The market can go through a flat period of 0% to slightly negative return. This period can be as long as 5 years. Next, the market may rise much more than average return to compensate the flat period. Although the average annual rate of return is positive, actual rate of return may be lower or higher than the average value.

If you borrow 80W, the interest rate is fixed, the payment is fixed. The maintenance cost will only increase. You may experience about 10-15% vacancy rate. If the next 5 years is flat, these constant expenses can be enough to make you bankrupt.

To be frank with you, I think you are just an amature investor. Most experienced investors don't buy a 100W house to rent out. This is crazy. Experienced investor always rent out affordable priced houses. The primary reason is to maximize cash flow.