Excellent route! There is no part of it that ought to be avoided our experience towing a TT. Don't expect to see much ocean anywhere. Yes, where do you plan to get onto 101?
If heading south from Vancouver, taking the ferry from Whidbey Island (turn right off I-5 at Burlington) over to Port Townsend is VERY nice and highly recommended. The 101 drive around the Olympic peninsula is a lovely drive but you won't see much ocean. Taking 101 down the east side of the Olympic peninsula is also very nice, a much shorter and direct route and you'll see Puget Sound in parts. To do the latter, head west just past Shelton. If you've got the time, I suggest taking a side-detour over to Ocean Shores for at least a part day while heading down to Astoria. Camping next to the ocean in Ocean Shores is a great experience.
Unless you are planning to visit Seattle, avoid it like the plague as traffic is pretty bad 24/7 and not fun when towing a TT.
The Astoria area is great - have fun!