Part of this is your application, the noise floor is going to be the first thing effected by EMI, but where you probably want to operate is considerably higher power levels, so you don't have to necessarily go all-out for noise reduction since the range it would effect probably isn't the one you'll be interested in. I don't think you're likely too far off of "just work" in terms of EMI, but there's certainly stuff you can do to minimize the risk. Please let me know if there's more information that you need, and thanks in advance for anyone who spends any of their time helping me out! Note that this is a one-off for my own personal use, and won't undergo EMI/EMC testing. I'm hoping to layout something robust and adaptable with extra footprints and myriad test points so that I can really dig-in and see what's working or what needs tweaking. It'd be really nice if this "just worked", but we all know that is never the case. Should I just alternate ground/signal/ground/power, etc? In terms of filtering, the highest signal speed is the 400 kHz I2C for the LCD, but the bargraph uses some 74HC glue logic, and I know both of those will have harmonics to be dealt with. This is an obvious bottleneck for the low impedance ground plane, which makes me wonder if I am best off simply running a bunch of extra ground lines for each connector? The bargraph, for instance, uses three signal lines and one +5V line. I'm currently planning on ribbon cables with IDC connectors, but I'm open to suggestions. Each one will be connected by a short (not more than 6" / 150mm) cable back to the main board.