1. There's nothing particularly magical about 'lifetime' but long tenure is appropriate to secure independence of the branch.
2. Meh. Don't really see this as a particularly problematic flaw, or why this would be so and not as to other legislative matters. (That said, see comment 6)
3. This is supposed to be hard. It's the foundational document that everything is subject to. And with that said, the only reason it's 'hard' is, frankly, because of the political divide of economic interests by geography.
4. I'm not sure I follow this one, either or in terms of the problem or the causal link you're suggesting.
5. If it were the national government, the problem would be accentuated because there would be one winner, who would really take all. Politics doesn't magically disappear by elevating it to the national level.
6. The power of the purse is sort of an interesting point, but for my money, the only reason the Senate is overpowered is due to the filibuster rule/custom, which is nonconstitutional and I would not lose sleep if it were eliminated.
7. This is bunk. 270 is 270. While I like the district allocation method NE and ME use, you still gotta get there, and us electoral stats have always been such that some states are 'safe' in elections. Beyond that, if it were really the case that only a few states decide things, I would not receive 1/100th of the spam texts that I do.