We use layout #1 for the layout bar at the top of the screen. I have a guildie creating a new logo. I do not want to give him administrative rights to the site. What are the ideal parameters of the jpg for the logo to have it fit the best?

For that layout, a with of no more than 400 pixels wide should be alright.

If it's bigger, you can always do the Layout number 4, or you can let the system auto-resize it to fix for you.