The Blue Ox 2-Point Weight Distribution system you're looking at would work fine but I don't think you're going to need a system that big.
I recommend checking out the Reese Steadi-Flex Weight Distribution System w/ Sway Control # RP66558 instead. This system has a tongue weight range of 400-600 lbs which seems like it'll be much better suited for you.
I do still recommend loading your trailer as if you were heading out and having your trailer weighed to get the official tongue weight... view full answer...