How big should I make my downpayment?

Its always best to have a bit of a cushion in case an unexpected issue comes up. The more down the better. If you can put enough down to do a 15 year loan is a huge savings over the span of the loan.

THIS IS a GREAT QUESTION! As a REALTOR I have seen very smart local lenders actually tell my clients to not put as much down because they may not be staying in a home as their forever home for more than 5-8 years and it does not make sense to put more money down when you can take that money and invest it in other areas for a bigger return! Also, there are recent changes to the lending regulations that may actually penalize some that are borrowing money because it could make your rate higher if your credit score is in a higher bracket. A good Local lender can give you specifics about these options based on the loan type and the amount that you are looking to finance and your credit score! So reach out to a good local lender to determine the best options.

That is a very personal choice. In order to make a decision, talk to your lender and get all the information from them of the various scenarios you are considering in order to make an informed decision. In all cases, you should have an emergency fund of at least 3-6 months of expenses kept solely for any unforseen expenses, separate from the downpayment amount. Hope that helps.