one of the first questions I'd ask is are you buying in a seller's market? If so, you may want to wait until the market becomes a buyer's market. You always save a ton of money just by buying low and have the seller's pay most of the transaction costs. If you are still wanting to get to 20%, it could make sense to hold off.

As for how much to put down, the minimum is typically around 3% ($6K for a $200K home). Of course, you'll need more to cover closing costs. $15K is probably sufficient, since sellers always cover commissions. You just need to structure the offer to ensure it doesn't exceed the $15K.

As for robbing the IRA or avoiding PMI, there are a few factors. The PMI payment for $200K is roughly $150/month. How long you'll pay that is a gamble. If the home prices are rising and you get to 20% equity within 3 years, you'll have paid an extra $5400 out of pocket. If it takes double that, then $10,600 out of pocket. If your home value sinks, then you may be stuck it.

In this case, you will need to get to $40K to be at 20% + a bit for closing costs. You'll probably need at least $45K to close instead of the $11K based on 3% down. That basically means that if you had $34K to invest, you'd need $283/month to get a 10% annual return. When you pay the PMI and increased mortgage cost ($312/month combined minus some tax savings).

I assume the IRA has already been taxed, so the return will be tax free? What's your average rate of return on the IRA? I'd hate to advise using tax sheltered retirement money as a down payment, but if the real estate market is thrashed then I'd say yes. If the market has been rising the last couple years and is at a high level, then I'd say wait until it becomes a buyer's market again.