Thoughts:
- Think it's obvious, but as noted above, Los Anchorage is nothing particularly special in itself; good jumping off place for other adventures, but not a destination in and of itself;
- April is not too early, although there may be snow on some of the roads at higher elevations;
- Hopefully, "mid-September" is when you're leaving AK, not arriving back in Idaho or wherever. In September (particularly mid- or later) you'll see an entirely different season in much of Alaska and the northern end of the Canada trip.