How important are the state house elections this year with the forthcoming redistribution of Congressional Seats?
It varies by state. It obviously doesn't matter at all in small states that only have 1 Congressman (Alaska, Montana, Wyoming, North Dakota, South Dakota, Delaware, Vermont [did I miss one]?). It also doesn't matter in the states that use independent commissions to redistrict. It matters a lot in states like New York, where if Republicans regain control of the State Senate (possible, though perhaps unlikely) or state house (longshot), the map will look very different than if the Democrats control those entities.
Two district states like Idaho, Hawaii, Maine, Rhode Island, New Hampshire and Maine probably dont matter either. There is not much you can do to change those districts.