Getting started with the Spirit theme

Hi, I just got started (finally logged in to play with the themes). I picked the Spirit theme and wanted to make a simple blog with featured photography. Are there basic resources I could reference to make sure I am doing it all right?

The issue I am having now is trying to determine how large the images should be in trying to design the page, and then overlaying clickable text menu links on the top. Any help would be greatly appreciated.

Lastly - it seems I will have to activate the theme when playing with Upfront? If that is the case then visitors to my site while I am editing would be able to see that I am working on something? Thank you.