I just realized
 

A lot has to do with your work. How would your boss handle it if you got a flat and were 30 minutes late? If they are OK with people having car trouble, why would they get upset if you had trouble with your mode of transportation?

Another thing you can do is try to mitigate the risk of breaking down. The most common problem are flat tires. You can virtually eliminate them by getting a tough tire, like Gatorskins and using a puncture resistant tire liner. Then all you have to do is just make sure you have the correct tire pressure every 3 days or so and you will not have to worry much about flats.

Other mechanical issues can be prevented by doing your maintenance. Wash your bike, lube your chain, adjust your cables, lubricate your bearings. Don't let things fester. If you have a frayed cable, replace it. If the chain is starting to stretch, replace it. If a bearing does not feel right, replace it. While bicycles are much simpler than cars, they still require some maintenance to be reliable. Be sure to have some basic items in your saddle bag so that you can fix minor issues like something coming loose.

Ultimately, do what you think is right for you. If you don't feel comfortable with riding the whole way both ways, then take the bus to work and ride home.

I suggest doing a test run of the actual commute during the weekend, which should resolve the mental resistance.

At first, start out early, like 30 minutes or an hour, to give yourself time in case something happens.

Mechanical issues other than a flat now and then can be mostly avoided and are usually pretty minor. If you pay close attention to the bike and maintenance, which I've found to come pretty naturally when you're commuting frequently. I'm more inclined to check everything over and deal with whatever comes up before it becomes an issue. Nevertheless, when I started I felt the same way and would take a lot of tools with me, even random replacement parts if I had them. There's nothing wrong with that, though eventually you pare it down to only what you really need.

Just a thought, but can you drive partway, park, and then ride the bike the rest of the way? Build up to the full distance while you build your confidence? All the planning and thinking in the world does not beat your personal experience from doing it

That is essentially what I did; started with a 2.5m (one way) trip, now doing 7 - 10 miles, each way, depending on how I feel.

Things I've changed, from the beginning, based on 'wisdom', based on 'experience', based on mistakes made:

-I don't rely on bungee cords to hold a jacket to a rear rack (lost jacket).
-I don't use an open, grocery-carrying style pannier to carry things (lost stuff)
-I do carry a packable rain coat.
-Spare tube, plus patch kit, which I (finally) trust that I can use, successfully.
-Know all the bike shops between car parking spot, and work.
-Have Plan B (and Plan C) in the event of major breakdown, or weather issue (haven't yet have to use).
-Triple check lights, brakes, tire pressure.
-Put all cycling stuff in panniers night before, put panniers where I will see then walking out the door.


...In other words, I've made plenty of mistakes, and learned from them. I used the forums as a leg up, but learned the most by doing things not perfectly, and then improving what I was doing.

Those are all good points. I biked most of the route while I was home (the hilly parts anyway.) The commute sort of breaks down like this:
7 Miles no traffic a few steep hills but nothing killer
3 Miles Moderately busy good sholder
5 miles no shoulder busy but good site lines and regular bike use. (this is HWY 99 from Creswell to Goshen if anyone lives around Eugene OR)
the rest is in Eugene; good shoulders, bike signage etc.

As to the work thing: I feel like if I am on time mostly then if I get a flat NBD; if I get a flat the first time I will never live it down. I need to build up some cred with my boss on that one. The bike came with commuter style tires and protectors, along with lights, tools and a spare tube (the guy was a boy scout I swear). So I think I am good to go. When traveling I assume an average speed of 10 MPH while my actual SOG is around 14 for long distances. That gives me enough time to not stress and enjoy the ride.