How much does 1 NEMcoin cost in btc ?
1 NEMstake ~ 35K Nxt. 35K Nxt ~ 2BTC. Approximately, cost of 1 NEMcoin is 2 BTC/ 1M = 20 satoshi.
2/1m = 200 satoshis.
or will it be
2 BTC 2000 000 = 0.00000100 BTC = 100 satoshi
Wouldn't that be a nice, round number, even hanging on the decimal and SI systems

This is only taking account of 1k stake. You should be dividing by 4 in reality
No, 200 satoshi is correct. Multiply this by 4 billion and that gives a marketcap of 4000 btc and places it at number 11 on coinmarketcap. With btc at $340 usd this could be cheap if it turns out to compete with nxt.
Has it been scarved to the stone that NEM will have a maximum of
4 000 000 000 coins ...
or will it be
8 000 000 000 coins.
If the latter option, then 100 satoshi is the correct one. And would it be better? ...as Buratino mentioned that 200 satoshi is too expensive, when thinking about the ROI.