Rain Barrels and pumps

I have questions that I hope someone may have had experience with and can offer suggestions-
I have a 55 gal rain barrel that is sealed (other that screened collection at the top).
I have not had much luck using the water from it to water my beds because my yard is sloped and roof run-off is at the low end of the yard, while most of my flower/herb/garden beds are at the top of the slope. Which means no water pressure, and quite a distance to travel (about 1/2 acre of distance)

This year I have decided to leave the barrel standing next to a stone wall at the top of the yard, and use gravity to water my top of the yard beds. I'm wondering 2 things-

1. Without the roof run-off will it be full enough (has anyone done this w/o roof run-off)?
2. I will still need a small pump, as the slope is not that great. As the barrel is sealed, and I don't wish to drill holes, I want to use an external pump (non-submersible). Has anyone tried this? Can you make a recommendation on a pump to use?

I am sooooo hoping to make this work this year and stop the municipal water use on the beds, so any suggestions are welcomed.