The backlight flicker you mentioned is normal (as well as other power oddities).
I second @Rex’s opinion that it is worthwhile testing on any known working image, if only to make sure the screen works before showing the unit some love. Given the error message you have pasted, you may also want to test the keyboard and trackball to ensure USB works, just in case.
If you get U-Boot working I encourage you to do a write-up and either post or hyperlink it on this forum.