Hmm don't know. Today we don't have any computer lessons (teacher is ill) so can't look the size up now. Though you can try something, it's somewhere in the site settings
Didn't think of text yet, maybe you have some ideas?
edit: lol the schedule changed now we have dutch on the computer.
Anyway the width must be maximum 1125(pixels), but can be less. Height doesn't matter (the page automaticly adjusts).
For text at least 'Instant Own', maybe some kind of slogan (maybe 'owns you where you stand', ..just brainstorming a bit
).