Thanks for this thread! I had to drop MATS in order to get the upgrade to install and now in order to boot.
I have to admit that I am clover "challenged" I have been trying to figure out how to make clover drop MATS routinely. I am using Clover Configurator 2 with clover 4220.
I have thought about doing a filter,too! The G5 is free breathing and that will bring in the dust.I looked around for filters and did not find that much. I picked up some wire form at an art supply store with the intent of making a filter. As you can see, I have yet to open the package.
Keep us posted on how your cooling solutions work out. I am contemplating cooling improvements for my G4. I expect that it will entail some sort of hole in the bottom similar to your layout.
Read all the builds that have been posted here and then decide how original you want it to be. The more original the more challenging it will be. Remember, once you remove the guts there will be lots of free flowing space there. Modern hardware does not need nearly as many fans as the original...
A motherboard tray is not necessary, but it can be nice. Lots of folks just epoxy standoffs for the motherboard.
Micro ATX is easy but the G5 is big enough to accommodate an ATX motherboard easily. You have to ask your self how much do you want to do yourself, how much do you want to spend and...