>>1266365>When is the best time of year?Now instead of later. It sounds like a good plan.
> Transplanting bushes?That takes a monumental effort depending on the bush type and size. The hole you need to dig to get it out is massive. You can reduce this to some extent by trimming 1/3 of the top of the bush before digging it up. This will help compensate for tearing up some of the roots. A dolly/hand cart is all you'd need to move them from one spot to another unless they are really old and huge, in which case you'll need a team of people to help you.
>30+ industrial repurposed plastic drumsAre those the 55gallon drums? If so, you can cut them in half to have 2 nice upright barrel planters. Some people split them lengthwise, but that means you have to design and build a frame to hold them up correctly. You can combine these two methods in this image. All you need is a pipe with holes in it, heat gun, jigsaw, and a glass bottle. You'd be able to plant in the sides and top while putting compost into the pipe over the season. FYI, the full size 55gal barrel planters are too tall and get too dry at the top and too wet at the bottom.