Not things to avoid, but a couple of things to see, unless you are on a tight schedule. With decent weather, the hills between Helena and Harlowtown are not too bad and an easy jaunt around the hills north of Billings. Early April, the snow is melting in Idaho........ the Big Creek drainage, Cabin Creek for sure, maybe Johnson Creek and the short runway at Moose Creek I'm sure will be open then.
If you make it as far as eastern WY on the first day and have some time, Gurnsey, WY (GUR) used to have self serve gas and a courtesy car. The guy that has the only hotel in town, is a pilot, and about a half mile south of town, there is a park where the Oregon Trail went by. The wagon ruts are impressive to see and just a short walk. If they no longer have a car at the airport, I understand the guy at the hotel is very accommodating with transportation, even to the restaurant for dinner.
If you happen by Bill's place in the afternoon, stop for lunch at Amana, IA, (C11) grass strip on the edge of town, no gas but about 2 or 3 blocks into town for 3 or 4 places with some family style German Food. (Weinerchnitzel is always a winner) You can pick up a couple bottles of local wine for the "We Made It" celebration back in NY.