Nice setup @haitch!
@Eq I currently only have a few usb 3.0 drives running off of a 7 port hub (only 3 used at the moment). 1 8TB Seagate and 2 Western Digital 8TB. I thought it important to make sure the drives are running off of an external power source and not the ODROID just to make sure they're fully powered and you have more expansion options. I'm sure it would work fine plugging just two drives into the front USB 3 ports though if that's all you had.
I'm still experimenting on getting the total round time (read & verify) down in creepMiner, but it's a bit tricky. Ideally I'm trying to keep the round under 60s if possible, which I'm setting as my "drive limit". You're probably fine if you're under 4 min though. The beauty of such a cheap system is that you can just clone it and run multiples with a proxy for relatively low cost.
Don't use the latest 1.8.0 creepMiner. It has an extra database function that really slows down the ODROID. 1.7.16 works fine.
I've posted a little testing data here: https://www.minesomeburst.com/valid-deadlines-last-360-blocks/
I'm also looking into porting Blago's miner to Linux along with some possible optimizations for the NEON instruction set. We'll see how that goes after I've got some benchmarking in.
I don't know if you really NEED the eMMC module, but it's working pretty well for me thus far. It gives a little extra speed for messing around with compiling with different options, etc. Micro SD is cheaper by far though..