IIRC it was to the House delegation which is a set of Congressional representatives, one from each state, who are to vote on the next president should there be dispute about the legitimacy of the state electors. At the time the Dems had a majority of the House but not a majority of the House delegation and so the hope was that kicking it to the House delegation could result in a Trump win.
Why would Trump kill the people who helped him stay in power? He ran on pardoning these traitors and won.
I don't think you're following here. The plan wasn't to take Congress hostage, it was to get Congress to overturn the results of the election and specifically to have Pence throw out legitimate Biden electors in favor of his fake ones or to have Pence use the chaos as a pretense to send the matter to the House Delegation which was made up of one rep from each state and thus a slight GOP majority at the time.
I don't think it was state legislatures but rather the House delegation which is made up of one Congressional rep from each state. Honestly I could be getting it wrong because we're getting into very nitty gritty constitutional procedure here. Its precisely this esoteric nature of the plot that allows Trumpers to either play ignorant about it or, in the case of the vast majority, legitimately be ignorant about it. I didn't know about most of this stuff until the wake of Jan 6th and even then only relatively recently.