On the plywood and 2 x 4 bin you need to allow for all of the loads you are going to encounter and make certain that the wood you are making the bin out of will not come in contact with water as it will wick and pellets will get ruined. Also be certain to allow for pellet dust caused issues (static charges and dust are not good playmates).
Agreed. I have a friend (carpenter) who will sanity-check my plans. I've lucked out that our basement seems to be fairly leak-resistant. The previous homeowner stated that he never had any dampness or leaks in 10 years. He could have lied, but the basement is mostly finished and I didn't find any signs of water damage. I'll include a form of vapor barrier however against the concrete just in case. I also have a dehumidifier to help with humidity in the summer.
I read that an exhaust port and grounded fill/exhaust lines are recommended for these setups. I'm not sure where else I may get static charge from. The exit pipe will be quite short and will drain into a bucket. There will be a ported "door" for cleaning as well as sealing the inside against leaks.