From a mildly educated foreign point of view, it is all very interesting.

As far as I can see, Flynn's evidence might be critical to any action against Trump.

If the committees in the US Congress are similar to Australia's, the Republicans will have a majority on the House Intelligence Committee because they have a majority in the House.

If they refuse to grant Flynn an immunity against prosecution, he will "take the Fifth" (I think that is the quaint American expression) and refuse to answer any questions (including what his name is). This might shoot the whole inquiry down in flames. However, if enough Republicans dislike Trump, they might vote with the opposition and give him immunity.

This will be further confused if the opposition Democrats decide they want Flynn's scalp and refuse to give him immunity.

Whatever happens with Flynn, if the inquiry does come up with enough to impeach Trump, the impeachment still has to be voted on, and needs quite a few Republicans to vote against a Republican President to succeed.

... and then, you have President Pence.

Best of luck, fellers ...