Your idea is a good one. Imagine you are doing individual square cakes. However you would do those is how you would approach the blocks. I’d definitely use pound cake, then layer the cake. Put in the freezer to firm up nicely before trimming them to the perfect square shape. My guess is that this will be the hardest process.
You can definitely ganache them. Because they are small you could try pouring the ganache over like you would on a petit four. I would do fondant panels on each side so that the shape stays nice and crisp.
Yes, very time consuming. Anything that small is always time consuming. Most places here are anywhere between $10-20 each for mini cakes depending on how much detail you put on them.
