Excellent points and absolutely fair questions. I can’t answer all of them, but let me at least address the first one, which I think is the only one relevant to the impeachment issue. The others are examples of why Trump may not win the Boy Scout award for good behavior, but are things that the electorate knew about and still gave him way more than 270 electoral votes.
Your specific hypothetical was:
Would you have been OK with Obama trying to get dirt on Mitt Romney from the Iranians?
I’d like to make a small change in that, substituting Egypt for Iran, because I don’t think we have been giving aid to the Iranians since before 1979. I apologize to the Egyptian for using their country in this analogy. To make it a solid analogy, let us suppose Romney’s son had no experience in irrigation, dams, or water systems and didn’t speak Arabic but was paid millions to sit on the board of an Egyptian dam construction company while his Dad was doling out US aid to Egypt. Under those circumstances, yes I sure would want Obama to ask the Egyptian President to have his government investigate. If Romney himself had overtly pressured the government with loss of US aid unless a Prosecutor was fired in six hours, I would want both of them investigated by both countries and also demand the US Congress hold hearings on the blatant conflict of interest.
My position is that the same standards ought to apply to both sides. We have too much corruption, too many conflicts of interest, and too much nepotism.
You keep saying “getting dirt on an opponent", but what if the opponent is dirty? A publicly announced investigation into corruption and influence peddling is not the same as receiving opposition research. If it turns out Hillary knowingly paid money from her campaign to Fusion GPS to Christopher Steele to get Ukrainian and Russian dirt on Trump, are you ok with that?