I drill all the holes anyway, so if I strip out a hole or break a screw, I can just use the other one. If you want to make housing units different size, or use larger or smaller modules, just follow these techniques as you work out your own layout. Once you have assembled a couple and are pleased with the results, make a template to speed your work. Use a piece of paneling or other sheet material, drill small holes at the screw locations for an awl or nail to fit through. Then just clamp it to your base block, poke through the holes to mark the locations, and you're ready to drill.
Most lumber sold today has fairly large growth rings, and accepts screws without splitting.
If you salvage some older, dry material with tight growth rings, you may have to drill lead holes for the screws to prevent the small blocks from splitting. I've read that you can expect your bee population to increase by five times each year. The units shown, made of one filled block and five empty ones, will give your work force room to grow. The modular construction means next year, you can easily disassemble it and use your own recruits to spread the good word. I actually had better recruitment than predicted, so you may want to place additional empty blocks in the area to capture all the potential.