Land Attrition: -95% as Kongo or Horde (with horde ideas, not gov type), defensive ideas and quality+exploration and humanist+defensive ideas
You forgot Quantity ideas for a further -10%. Also Arabian or Siberian gives -15% which is also enough for -100%. Also chickasaw w/ the native american bonuses can get a base -30% bonus for the maximum possible of -115% (not useful but lets you ignore another bonus), and any native can get -100%.
The game will display you as taking negative attrition (i.e. gaining forces from attrition) but it acts as 0% attrition everywhere. This means you can in fact completely ignore supply limits and theoretically instant-wipe 100k Prussian/French stacks if you mustered 1M troops together thanks to the instant wipe at 10:1 odds rule. I'm sure someone will have fun completely destroying France without losing a single soldier.
Advisors cost: - 98%, as colonial nation, with innovative ideas, influence+innovative, innovative+dip and innovative+plutocratic policies trading with tea.
Pueblo can do better with -50% from the Native American building and -25% from their ideas which beats -33% from being a CN. Not sure if it stacks beyond 99/100% though so the point may be moot.
Morale of armies: +90%, as Shiite France or Brandenburg, with defensive and plutocratic ideas, quality+religious and religious+quantity plicies, and noble republic, dictatorship, merchant republic with aristocrats faction or revolutionary republic governments being a defender of the faith.
Unreformed Native Americans with their generic ideas get +15%, with a further +30% for being in a federation and +10% for their native military ideas. Theoretical maximum for an unreformed Native American who becomes Shiite and gets the ideas/policies is +115% I believe.
Land maintenance modifier: -95% as Scotland, with defensive, economic and quantity ideas, and administrative+quantity policy and grain depot with merchan republic government with aristocratic faction trading with salt.
Native Council government type gives -50% which will easily push you over the edge to -100%. I believe it caps out at -99% but that's still 5x better than -95%.
Building cost: -70% As Hindu (with Ganga as PD) Portugal, with economic ideas, aristocratic+expansion policy.
Pueblo w/ native bonuses can get -85%.
Probably one or two other minor bonuses I missed where Native Americans can exceed normal limits.
Recommendation: Someone play a Native American game that stays unreformed, gets -100% land maintenance cost and -100% land attrition, then doomstack to (nearly) infinity. Pueblo might be a good choice since they should be able to ride +3 advisors ASAP (you need tech for policies and ideas), but Cherokee could also be a good choice.