Learn English – Looking for an idiom regarding trust

Some options from a thesaurus (some better than others): peanuts, crumbs, chicken feed, chump change, nickels and dimes, pittance, small potatoes, scraps, drop in the ocean, trifle.

Of these, "peanuts" and "small potatoes" are probably the ones closest to appropriate in your sentences.

I've never heard the phrase "set the heather on fire" before either. (Though as we speak, a nature preserve that borders my property is being set on first as some sort of environmental measure. They promised not to burn down my house in the process.)

If you mean "sensational" in the sense of "causing widespread interest and excitement", like might be caused by a radical new invention or a political movement, then "set the world on fire" is a closely-comparable phrase. Another would be "turn the world upside down", though I think that's getting antiquated. Or "upsetting the apple cart".

If you mean "sensational" in the sense of "acting wild", like a wild party, then "paint the town red" is a common American idiom. Also "running amok".