Hi. I'll be visiting Portland for the first time with my family during the last two weeks of July. I'd like to drive along the northern coast to experience the natural scenery and historic sights. I need some help deciding: (1) which stretch (or stretches) of coastline is the most scenic, and (2) what towns/areas are good stopping points for food, drink, shopping, etc.

My recollection is that the the scenic coast is south of Tillamook.

OK, I am sure I will get a LOT of flack from all the coastline purists/experts BUT it is pretty simple if you drive north west from Portland to Cannon Beach and go south from there. C-Beach has one of the several so-called "haystack rocks" which are pretty iconic IMO. Cannon Beach itself is full of the usual art galleries (of various quality levels), restaurants, bars, etc., etc., IOW the USUAL commercial beach stuff. People are going to tell you how BAD the place is, how CRASS it is, and how UN-scenic and UN-unspoiled it is, and the rest of it. But then there's this rock, and that surf and those birds, and that wide beach...

An alternative: drive west and drop into the water wherever...you will not regret the trip I am certain.

How many days are you spending in Oregon? If you have 11-14 days, you can see a lot of the western half of the state including Crater Lake and the waterfalls in the Columbia Gorge.
I will never stay in any coast hotel that has a 2 night minimum stay. The town I like on the northern coast is Seaside which has a nice "prom" with a wide beach.
Just off the southern end of the Prom is a monument showing where members of the Corps of Discovery boiled seawater for salt to cure the meat for the long trip back to St. Louis.
Make the stop at the Tillamook Cheese factory for good ice cream and cheese.
You may be interested to visit the Oregon Coast Aquarium just south of the big bridge at Newport.

What's your preferred drink? What kind of shopping are you looking for?

I consider Portland to be superior in those respects to anywhere on the coast. The coast is really all about the beach, the views, and the corny tourist activities. My favorite town is Cannon Beach. Best place there for food and booze would be either Fultano's Pizza or Castaways, depending if you prefer beer (former) or cocktails (latter). Cannon Beach does have boutiques, but mostly art, overpriced casual clothing, beach themed things, etc. It's "unspoiled" in that carefully contrived way that many historic districts are "authentic", if that makes any sense. I know a lot of people don't like it but more tourists result in more "disneyfication", which results in more shopping, better food choices, etc.However, the bakery, candy shop, and ice cream parlor have all been around for a long time, and those businesses plus the beach make Cannon Beach a can't miss place.

A relative lives in Newport, OR, so I've spent time down there, and that area is just as beautiful in a different way. More to do than in Cannon Beach, possibly, but not very much shopping and the restaurants didn't impress me that much. The lighthouses are great, though, as is the Devil's Punch Bowl. I really enjoy the drive from Cannon Beach to Florence, approximately. Not a big fan of the south coast.

...to experience the natural scenery and historic sights.

A day trip? One night? Two? Makes a big difference.

If your time is limited, either no overnights or just one, then I'd do a loop that includes Cape Meares near Tillamook, up to Ecola State Park near Cannon Beach, then north to Astoria and over the awesome mouth of the Columbia to Cape Disappointment on the Washington side. You'll get fine scenery, lighthouses, waves on rocks, the whole deal, plus terrific historic sites near Astoria and especially Cape Disappointment (Lewis and Clark). Then I'd follow the north bank of the Columbia (historic, scenic, off the beaten path) east back to the Portland area.

If you have more time, then you could modify your route to include (if interested) some of the lovely vineyard country along 99W near McMinnville in the Willamette Valley, or aim further south and hit the coast around Newport, where there are other pretty coastal sights.

With even more time (now talking in terms of four days or so) you could shoot down I-5 to US 199 at Grants Pass, then out to the California coast through some beautiful and impressive redwood groves, then back the whole length of the Oregon coast, which has several spectacular stretches, the most beautiful of which (IMO) is the southernmost 70 miles or so, between Brookings and Port Orford. But again, this would take a substantial time commitment, so some indication of how long you have would be useful.