Should I hold the mortgage on my house balloon at 4% on 350,000 mortgage for 5 years with only a 25,000 down payment]

Ballons are a bet, current rates are better than 4% and who knows what the market will be when the ballon busts. This is only a good idea if you intend to sell before the ballon pops.

should I hold the mortgage on my house balloon at 4% on 350,000 mortgage for 5 years with only a 25,000 down payment]

When did you take out the mortgage?
What is the rate of the mortgage based on?
What is your credit score with the 3 credit reporting agencies?

The downpayment really has nothing to do with whether you should refinance now or not.

If you are lucky and your house doesn't fall underwater, and you don't plan on living in that house till the balloon payment date comes, then it might not be such a bad idea. But if you are looking at the place you plan on retire, or you are unsure whether the area will increase in price instead of decreasing, I would be very against getting a balloon loan.