Would you go shopping without knowing how much money you have or can afford to spend? Then, why would you go house-hunting before knowing what you can qualify for. Savvy home buyers will secure a mortgage pre-approval before even engaging a realtor. Otherwise, you may go around town without knowing what you can realistically afford or worse still submit an offer which you might not be able to honor. In other cases, the seller's agent might not even consider your purchase offer if they figure out that you haven't secured a pre-approval.
So, I will highly recommend that you secure a pre-approval (start here); one which factors in limitations imposed by Stress Test! This will keep you focused on homes within your price range. Plus, you can possibly lock the rate for a specific period of time.
Reach out to me if you have any questions regarding pre-approval or the '10 Steps from Start to Furnish'.