Isn't the tradeoff with static nodes is this coin becomes more centralized relative to bitcoin, to a max number of 650 static nodes?

How will static nodes handle DDOS protection?

If there is a price spike and 90% of static nodes owners liquidate, won't the network be much less secure?

Long term turnover of static nodes will eat away at the static node count over time. I don't think freezing the static node count from an early block is a good idea.

Sooner or later you will have to deal with turnover. You could setup a lottery, or static nodes compete on price, or a first come first serve basis: i.e. 300 nodes max, if the number drops below 300 then the wallet that has been signalling for static node upgrade the longest is upgraded to static node on the network.