just to add to what Lugia said - you could probably get away with a single rack wart (power module) to power both rows - although much easier with a single case
sometimes when trying to do things cheaply you need to spend more upfront to actually make the savings in the long run - it's like buying from a warehouse store (like costco) as opposed to a deli - work out cost per hp for the DIY powered case - and then work out how much a Mantis costs (I checked Mantis at sweetwater the other day at $335/204hp = $1.60/hp ish) and it's a respected case with good power etc etc and it's still portable, unless you are a small child
the easiest way to make a small eurorack system is, like how to make a small fortune, start with a big one!!!
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities