This is a great piece. I too started a company just 5 months ago. Fully bootstrapped and now con track to do 7 figures this year. Cash is king. You'll also be protected from the bubble when it goes BOOM :).
For (almost all) photos, JPGs are smaller and therefore load quicker. Its compression is much less noticeable in photographs, and therefore the size savings are usually worth it.
For logos, text, geometric imagery, etc, you generally need the image to remain relatively undistorted, so PNG is the way to go.