As you mentioned, it is surprising how often you can get multiple flat tires on while riding, particularly on longer sprints. The tip about bringing a patch kit in your bike repair kit can be incredibly helpful if you’ve already had one flat tire. I agree that all you listed seems like an awful lot to carry, but it’s always better to be safe than sorry, isn’t it?

A bicycle costs anywhere from $250-$9,000 depending what type and quality of bike you want. A utility bike from a department store might cost $300-$500, but experts caution that it will be quite a bit heavier and not as well constructed as other bikes. For a durable, lightweight bike with front-suspension and decent parts, it’s reasonable to pay $750-$1,200. You might be able to pay slightly less, but expect to need some repairs after several months of heavy use.

The thumb test is the fine art of pressing on the tube with your thumb to see if it’s inflated. During testing, I took a pressure reading out of curiosity, and to the touch, road tires feel fully inflated around 30 psi. How pathetically sad—30 psi!—when you’re probably trying to reach at least 60 psi on a mountain bike, 70 or more on a hybrid, and it only goes up from there.
Yes, bicycle shops generally provide repair services. A typical list of offered services includes regular service/adjustment (including safety check; and  brake, drivetrain, and tire inspection); premium, and annual service, which is a more extensive tune-up. More specific repairs include drivetrain tune-up, brake system tune-up, flat tire fixes, brake repairs, cleaning and touching up the bike frame.

For the budding mechanic:  A good pocket sized repair guide.   One good option is the “Pocket Guide to Emergency Bicycle Repair”  by Ron Cordes and Eric Grove.   It’s only 3.5×4.5 inches and a half inch thick.   I don’t carry this myself, but for someone who’s new to this whole bike repair business, it’s really helpful to have. A future blog post will cover this book in detail.
If you’re going to use the chain whip you just made, you’ll also need a way to get that cassette off. A lockring remover is a must-have; unless you use one of the shady removal methods I’ve seen on the internet—which I wouldn’t necessarily recommend unless you don’t care much about the condition of the wheel after you use them. I recommend Park Tool’s iterations here that cost about $6, but you’ll need to buy the specific one for your brand/type of cassette. (By the way, I’m assuming you already have an adjustable wrench laying around somewhere to use with this tool. If you don’t, well, you’ll need one of those too.)
We focused on tools that would be useful to a commuter—someone trying to use a bike as a functional way to get around town, as opposed to riding recreationally (road biking and mountain biking). That said, it’s a wild and wooly bicycling world out there, and the streets are packed with so many different bikes, all shapes and sizes, new and old. Customizing your flat-fixing kit has advantages over buying a preassembled kit that always contains a tool (or two or three) that’s a piece of junk, or you don’t need. Or it’s missing something you do need. If you build your own kit, at least you know everything works. And you can add only what’s necessary for your specific bike without ending up with stuff you don’t need.
Brakes come in a variety of designs depending on the age and style of your bike. Rim brakes offer more modulation but have less stopping power, so are more suited to riding on the roads. Disc brakes can provide huge amounts of stopping power so are best suited to off road riding, although ‘V’ rim brakes are also well suited to mountain biking. All brakes use a friction system to stop the movement of the wheel, so regular checks of the contact pads should form part of your regular cycle maintenance.