I ride almost exclusively on single lane country roads, but they're not crowded so I won't comment on that, other than to say, if there are shoulders that are safe to ride on, I personally do so, but don't be bullied into riding in unsafe spots (potholes, broken glass, loose sand, rutted snow, etc, things that will cause you to lose control or blow a tire).

If there are places in the road where it's not safe for cars to be passing you (like around corners on lanes too narrow for them to safely pass you without crossing the center line) then you're smart (and within your legal rights in most states) to "take the lane" - ride far enough to the left that drivers realize that they can't get around you, and make them wait until you get past the obstruction, then move right and let them past. Everyone's primary responsibility on the road is safety, not getting anywhere 3 seconds faster.

If there are alternate routes, investigate them. The best route in a car is not necessarily the best route for a bike. Remember that things that really slow down a car (like driving roads with 30 MPH speed limits instead of one block over with 50 MPH speed limits) don't affect a bike's speed but there will be less traffic so on a bike, that's the best route.

If your route is like mine, there may just not be any reasonable alternate route.

Type of bicycle isn't super important except that it should be comfortable for you to ride the 2 hours a day you're going to be in the saddle. I ride a hybrid, which has flat handlebars, a frame that allows me to sit more upright, and has skinny tires. Fat tires like you see on "mountain bikes" just slow you down and make you work harder if your commute is all on pavement. But some people like road bikes with drop handlebars, etc. It's a personal choice.

I paid $300 for my hybrid, put probably another $400 into accessories (I now have a pretty high end headlight, etc). You should be able to get started with between $0 and $100 in accessories-for $0 you're just dumping your stuff in a backpack; for $100 you're buying a modest head and tail light (NOT OPTIONAL if you're riding in the dark!!!!) and a cheap rack and panniers). Eventually if you ride in the rain you're going to be a lot happier if you have fenders.

I didn't buy all that stuff at once. Buy stuff as you find you need it, after looking here and elsewhere for advice and different available options.

I hope you come to love bicycle commuting in its own merits. I started out for several reasons, but honestly right now I like it so much that I'd still ride my bike even if someone gave me a car and fuel for free. For one thing, at 43 years old I look better and am far more fit than I ever have been in my life, even when I was in college. And I enjoy riding a bike way more than I ever have enjoyed driving a car.