I'd really appreciate any guidance/advice/suggestions/etc. Some specific questions:
1) I think I want a road bike, does that seem correct? It definitely seemed easier than the mountain(ish) bike I test rode despite the fact that the bike shop recommended the heavier bike for "Seattle's bumpier roads"
I think there are a few types of bikes that would work for you:
1) a hybrid bike (the flatbar roadbike style, not the comfort hybrid style)(like the specialized sirrus another poster mentioned)
2) a less sporty dropbar bike, like a lower end cyclocross bike, touring bike, or older used road bike. These bikes typically have more relaxed geometry (nice happy medium between comfy for commuting and aerodynamic enough for exercise rides) clearance for larger tires (which will help on bumpy roads) and eyelets to mount racks and fenders (essential if you are commuting. do not buy a bike you cannot easily mount fenders to). Conversely, dedicated modern road bikes are impractical for commuting - can't fit bigger tires, difficult to attach full fenders, and the geometry is good for aerodynamics but not good for comfort and keeping your head up in traffic.
3) a mountain bike with a rigid fork (no suspension) and the knobby tires swapped out for slick tires.
2) Any bike recommendations/thoughts on bicycles? Things to think about? I've been reading "best bikes under x" articles on bikesmarts.com but not sure how applicable it is or how trustworthy the advice.
Buy a bike locally (craigslist or local bike shop) so you can test ride it. Fit is important, and something you can't determine from someone else's review.
Since you are new to biking, I would suggest starting with a used bike off craigslist or from a bike recycle type shop. Your bike preferences might change. If you get a used bike and later decide you want a different type of bike, you can probably sell it for near what you paid. I know you are tall, but Seattle is a big city with an active craigslist so you probably have a better chance of finding one to fit than most of us. Or if you can't find something used a hybrid flatbar roadbike type might be a good new option because they are typically less expensive.
Disc brakes are nice for rain but not necessary. If rim brakes seem weak, typically adjusting them or getting new brake pads (around $10, the salmon kool stop pads are extra good for rain) will improve things. If you do get an older used bike, make sure the rims are aluminum, not steel (or factor in the cost of replacing the wheels). Steel rims (found on some 1970s and 1980s bikes) are rubbish for braking in the rain.
Definitely buy fenders. Full fenders, not those little clip on ones.
3) Is carbon fiber really all that? If its a giant jump, I'm fine with paying for a carbon fiber bike but if its a tiny improvement for a giant leap in price I'm less interested.
Carbon is completely unnecessary for the type of riding you want to do. Worth it for racers, not needed at all for commuting and relaxed exercise type bikes. Heck, I even ride more aggressively with a local group and keep up on my steel framed bike.
4) What should I know going into a bike store to buy a bicycle? I'm hesitant to go into a bike store and shell out 1k for a bike with my limited domain knowledge. Odds are that I'll be treated well and get good advice but without any knowledge of my own I'm completely in their hands.
Some bike shops tend to skew towards racing, and might try to sell you an aggressive road bike when you say you want a commuter. If that happens, leave, and try to find a shop that has more of a commuting or touring focus. Test ride the bike (ideally up and down hills, and for at least 20 minutes) and pay attention to comfort. Don't buy from a shop that wont let you do a real test ride. If a bike doesn't feel great right away, a good bike shop should adjust the seat and handlebars for you to get a better fit.