It'd be better to selectively eliminate targets and then observe the results before acting again. Strategic and deliberate, not indiscriminate or rushed. A lot of them are super old too, so a heart attack or stroke isn't exactly going to raise any eyebrows if they're spread out a little. If you go around chain slaughtering hundreds of people in a niche environment (rich & powerful), people are going to take notice and start looking into things. And if a Death Note actually existed, that would imply that there are people who could track such a thing, therefore necessitating cautious and deliberate use rather than acting like a manic psychopath.

Also I checked how much ¥10m was in USD. It's 69,427.60 as of Monday 12:40am CST. So close.