With regards to point 2 : having too many masternodes will slow the masternode network. If the collateral of 1000 Dash would be cut to 500 Dash
and our current masternode operators double their masternodes because of this, we could be looking at 10.000 masternodes. This would be too much for our network.

I am not sure how exactly or where exactly it slows down, maybe in the block propagation area or in the quorum area ?
Also the time between MN payments would double (from 8,5 days to roughly 16 days).