First home buyer, financing questions

I think we would be good with paying around $1200 monthly mortgage fees (with all other property fees included like tax etc.)

You probably can't get a $250k house for $1,200 a month including taxes and insurance. Even at a 4% rate and 20% down, your mortgage payment alone will be $954, and with taxes and insurance on top of that you're going to be over $1,200. You might get a lower rate but even a drop to 3% only lowers the payment $90/month. Getting a cheaper house (which also reduces taxes and insurance) is the best option financially.

What to do with the $15k that I have?

If you didn't have a mortgage I'd say to keep 3-6 months of living expenses in an emergency fund, so I wouldn't deplete that just to get a mortgage. You're either going to be

Since 1) the mortgage payment would be tight and 2) you aren't able to save for a down payment, my recommendation is for you to rent until you can make a 20% down payment and have monthly payment that is 25% of your take-home pay or less. Which means either your income goes up (which you indicate is a possibility) or you look for less house. Ideally that would be on a 15-year note, since you build equity (and reduce interest) much more quickly than a 3-year note, but you can get the same effect by making extra principal payments.

Also, very few people stay in their house for 30 years - 5 years is generally considered the cutoff point between renting and buying. Since you're looking at a 10-year horizon it makes sense to buy a house once you can afford it.

When you say "apartment" I take it you mean "condo", as you're talking about buying. Right or no?

A condo is generally cheaper to buy than a house of equal size and coondition, but they you have to pay condo fees forever. So you're paying less up front but you have an ongoing expense.

With a condo, the condo association normally does exterior maintenance, so it's not your problem. Find out exactly what's your responsibility and what's theirs, but you typically don't have to worry about maintaining the parking areas, you have less if any grass to mow, you don't have to deal with roof or outside walls, etc. Of course you're paying for all this through your condo fees.

There are two advantages to getting a shorter term loan: Because you owe the money for less time, each percentage point of interest is less total cash. 1% time 15 years versus 1% times 30 years or whatever. Also, you can usually get a lower rate on a shorter term loan because there's less risk to the bank: they only have to worry about where interest rates might go for 15 years instead of 30 years. So even if you know that you will sell the house and pay off the loan in 10 years, you'll usually pay less with a 15 year loan than a 30 year loan because of the lower rate. The catch to a shorter-term loan is that the monthly payments are higher. If you can't afford the monthly payment, then any advantages are just hypothetical.

Typically if you have less than a 20% down payment, you have to pay mortgage insurance. So if you can manage 20% down, do it, it saves you a bundle.

Every extra dollar of down payment is that much less that you're paying in interest. You want to keep an emergency fund so I wouldn't put every spare dime I had into a down payment if I could avoid it, but you want the biggest down payment you can manage. (Well, one can debate whether its better to use spare cash to invest in the stock market or some other investment rather than paying down the mortgage. Whole different question.)

"I dont think its a good idea to make any principal payments as I would probably loose them when I would want to sell the house and pay off the mortgage" I'm not sure what you're thinking there. Any extra principle payments that you make, you'll get back when you sell the house. I mean, suppose you buy a house for $100,000, over the time you own it you pay $30,000 in principle (between regular payments and any extra payments), and then you sell it for $120,000. So out of that $120,000 you'll have to pay off the $70,000 balance remaining on the loan, leaving $50,000 to pay other expenses and whatever is left goes in your pocket. Scenario 2, you buy the house for $100,000, pay $40,000 in principle, and sell for $120,000. So now you subtract $60,000 from the $120,000 leaving $60,000. You put in an extra $10,000, but you get it back when you sell. Whether you make or lose money on the house, whatever extra principle you put in, you'll get back at sale time in terms of less money that will have to go to pay the remaining principle on the mortgage.