Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Should I buy a house or am I making silly assumptions that I can afford it?
The rules of thumb are there for a reason. In this case, they reflect good banking and common sense by the buyer. When we bought our house 15 years ago it cost 2.5 times our salary and we put 20% down, putting the mortgage at exactly 2X our income. My wife thought we were stretching ourselves, getting too big a house compared to our income. You are proposing buying a house valued at 7X your income. Granted, rates have dropped in these 15 years, so pushing 3X may be okay, the 26% rule still needs to be followed. You are proposing to put nearly 75% of your income to the mortgage? Right? The regular payment plus the 25K/yr saved to pay that interest free loan? Wow.  You are over reaching by double, unless the rental market is so tight that you can actually rent two rooms out to cover over half the mortgage.  Consider talking to a friendly local banker, he (or she) will likely give you the same advice we are. These ratios don't change too much by country, interest rate and mortgages aren't that different. I wish you well, welcome to SE.