You need to remember, mid Sept on it going to start getting cold, many of the parks east of the Cascades will start closing.
Now, best to see the coast north to south.
Central Oregon is best enjoyed July to mid September.
Crater Lake, early September at the latest. Again cold, park attractions start closing after Labor day.
my suggestion, come maybe a month earlier, take I80 to Reno, 395 north. First stop maybe Goose Lake state Park, NW out of Lakeview on 31 past the reminants of the vast inland lake that covered the west from central Oregon to Death Valley some 10,000 years ago. Visit LaPine state Park where we will be hosting. You can get a few nights no problem after Labor day. 97 north to I84, through the Columbia river gorge. Visit Timberline Lodge on Mt Hood. In Portland take I205 north to I5 to Longview, WA. Cross the river joining US30 to Astoria. Here you can join US101 south.