I will recommend you make the holes about 3 to 5 mm deep. Remember that you are limited by the reach of the Dremmel cutting disks you are going to use, so no point in making them 10mm deep..... you won't be able to reach in that far...
the hole diameter about 4mm, which ever is easiest for you... don't worry to much about the VDFC stuff... it's a nice "feature" and all, but to be honest.... even Bill will be hard pressed to prove it to be as effective as it sounds...
even though it is based on sound theoretical principle...
for your efforts, you can make all the holes the same...
Aluminum in this fashion... and I'm once more forced to pimp myself, (sorry)
will probably outperform any mass produced commercial block today.... probably.... this is not a fact... I'm pimping, remember...
one thing is darn sure, making this kind of block in aluminum is easier than cutting butter. Aluminum is the easiest metal to drill holes into.... so yes... on that aspect, it will for sure outperform anything....