Question: Edit: everyone who's answered has been very helpful -- I tried to select all 3 answers as "the" answer but in the end it only let me choose one. Thanks to all!

I'm interested in purchasing my first pair of clipless bike shoes, principally in order to get the bike fitted properly, but also for performance reasons. I've put it off until now because I've been a bit nervous about getting stuck and falling over.

I'd welcome your recommendations on what to look for, how they should fit (in comparison to regular shoes, as well), whether there are any types or brands that are 'safer' (easier to unfasten from the pedals in an emergency), and whether there are any tips you can offer from your experience.

For what it's worth, I have a Giant gravel bike which I'm riding solely in asphalt at the moment, but am thinking of moving to a road bike one of these days.

Thanks in advance

Answer: 
One minor thing may be worth mentioning: different brands tend to make shoes that fit differently. From your other footwear, you may have got the sense that your feet are relatively wide or narrow, or you may have got the sense that they're relatively high volume (aka high instep). If you have feedback like this, ask someone at the bike store for help. However, be aware that not everyone at the store may be knowledgeable about this, because bikes and human bodies are complex and not everyone may know everything. If your feet are especially hard to fit, ask for someone knowledgeable.

My impression is that Specialized, Shimano, and Lake have tended to have slightly wider toe boxes, i.e. the front of the shoe. Sidi shoes in general and most Giro models tend to be narrower. That's not a comprehensive list, it's just what I recall. Many brands make wide or high-volume versions of their shoes if you want to go that route, but bike stores may not have those versions in stock.

If you fall or crash, my experience has been that you come unclipped in the process, even if you have set the release tension relatively high. I realize that a non-cyclist might think that this sounds oblivious to danger, but I can attest that it is so.

A last minor point: there is absolutely nothing wrong with 2 bolt shoes on road bikes if you want them. If you're with a serious roadie group, you will be going against convention, but you can decide if that matters to you or not. I subjectively feel like my road pedals are a bit more stable than my MTB pedals, but the difference isn't large. I'm not sure it would be detectable in a lab. I don't believe that an XC mountain bike shoe is more flexible than a road shoe of the same price point, although I have no experience with non-XC shoes. On my smart trainer, I've done functional threshold power tests on both road and MTB shoes pedals, and performed pretty closely. My off-road shoes have a nylon sole, vs the mid- to high-end carbon sole on my road shoes to boot. I also don't perceive a huge difference between power transfer in each shoe.
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> I'm interested in purchasing my first pair of clipless bike shoes, principally in order to get the bike fitted properly, but also for performance reasons. I've put it off until now because I've been a bit nervous about getting stuck and falling over.
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Don't be nervous. You'll learn the unclipping motion instantly. I have never crashed due to not being able to unclip quickly enough. Actually what is hard with clipless pedals is clipping in, sometimes it takes a second or two. But unclipping is easy.

The most important feature you want to look for is that you must be able to walk on the clipless shoes like you walk on regular shoes. An unfortunately large fraction of clipless pedal systems has protruding cleats that prevent walking. So you can't stop and buy something to drink at a grocery store ... unless you like to walk like a duck.

Fortunately, Shimano sells SPD pedals (regular SPD, not SPD-SL) that has the cleats embedded in the shoe in a manner that allows walking on the shoes.

With SPD, you can select single release and multi release cleats. Single release cleats allow unclipping only for the intended unclipping motion. With multi release cleats, you can basically unclip using any motion. I recommend single release cleats. It's not that hard to learn the unclipping motion. With multi release cleats, there's the problem that regular forceful pedaling can cause an unintended unclipping event, causing you to crash.

The Shimano SPD pedals have a tension adjustment screw so you can set the tension really loose for training clipless pedal use but you'll want to tighten it later when you have learned how to clip in and unclip.

My recommendation for the pedals is PD-T8000 because they have the mandatory pedal reflectors required by the law in many jurisdictions, and they also have a regular side that allows you to ride on any shoes, not just clipless shoes. You might think having clipless side on one side only would be bad because you never know which side is up, but these PD-T8000 pedals have a heavy side and a light side so when stopping they are in a well-determined position. So this allows you to time putting your feet on the pedals in such a manner that you always repeatedly hit the side you want to hit.

You can select shoes from Shimano or from some other brand, but do ensure they have the two-bolt attachment for SPD cleats. At least Shimano shoes are sized such that a given size is sold with a bit larger number so the usual advice is to select one size up. For example, my regular shoes are size 43 but I use size 44 Shimano shoes.

Also if you ride at 5 degrees Celsius or colder, you'll want to buy a separate pair of shoes that are intended for cold weather, and if you ride at arctic temperatures you'll need a third pair of shoes for extreme cold.