So the way i calculate it....as soon as there are more than 100 MNs, you'll need to either mine or purchase additional TUN every 10.4 days to maintain sufficient MN collateral ?  Thanks but no thanks...

Block time (sec) = 90
Blocks/day   = 960
TUN mined per Block = 5
TUN minted per Block (MN) = 5
TUN mined per Day = 4800
TUN minted per Day (MN) = 4800
Days per 10,000 Blocks   = 10.4
No. MNs = 101
MN profit per 10,000 Blocks = 495