1. Your choice of martial art is going to be limited to what is available to you. If there's no school of a particular style near you, you won't be able to train in that style. That being the case, it doesn't make much sense to research all the martial arts styles out there in search of the "best" (in the abstract) style -- you're much better off looking at the styles that are actually available to you, as expressed by the schools that are to be found in your area. FWIW, that's how I got into aikido: I moved to a new town, and the only good martial arts school here was an aikido school. Rather than continue training in another style that I already knew and might have preferred, I chose the good school that was actually available to me.
2. As Matthew says, there is no concise, discrete "philosophy of aikido". In my experience, philosophy plays a minor role at best in day-to-day aikido training: most senseis don't spend a lot of time lecturing on aikido philosophy and what it all means. Likewise, most schools don't focus on esoteric practices such as meditation, which typically takes the form of a token "moment of silence" before or after class, although some dojos do have zazen sessions. If your primary interest is philosophical topics or esoteric practices, you will probably find more satisfaction if you go after those things directly rather than try to pick them up through aikido.
3. Likewise, character traits such as self-actualization, respect, harmony, focus, self-awareness, etc. are not taught as such in aikido training, nor in any other martial art that I have encountered. This may come as a shocker, because it seems like every martial arts school just can't resist trotting out these words and phrases in their advertising
They're very effective bait for parents who want to give their children a magic pill to give them all these positive character traits ("Hmm, little Bobby is awfully impulsive, and he has trouble focusing...I know! I'll sign him up for karate lessons!"), but a martial art doesn't teach these traits -- sensei isn't going to sit the class down and work on their harmony or whatever. Now, it does seem to be the case quite often that people who train in a martial art, and who stay with it for a decent period of time, do develop or enhance some positive character traits -- but it doesn't happen via the magic pill method. I believe that these traits can be learned
through martial arts training, or through many other practices, if you stay with it and are honest with yourself in your training. The combination of persistence and honesty and time tends to get you closer to yourself, I guess, is the best way I can express it. But it's really nothing like taking a Harmony pill and a Respect pill and a Self-Actualization pill, and there's no way to explain to someone at the beginning of the process how they'll feel when they come out the other end.
4. Self-defense: you say that you want to know how aikido would do in a "random street encounter" or "if something were to happen". That's a bit like walking into a hardware store, picking up a random tool, and saying, "Hey, is this tool any good?" If you did that at my local general store, the proprietor would probably say something like, "It's pretty good for driving nails, but it's not so good for shoveling snow. If you want to drive nails, you're in luck; if you want to shovel snow, the shovels are over in the barn; and if you don't know what you want, any tool will do." Compared to some martial arts, aikido is a complicated tool: it takes a while before you have the skills to use it outside of a controlled partner-practice situation. So, if you're routinely going into bars and getting into fights, or if you work as a police officer or a bouncer in a bar, maybe it's not the best tool for you. On the other hand, it's worth considering whether you need a self-defense tool at all. Yeah, yeah, I know, "just in case" -- and I'm sure that there's someone in southern Alabama who bought a snowblower "just in case" it snows two feet there. Most of us would look at that and say that it's not a worthwhile investment for an event that probably happens once a millennium. Likewise, most of us aren't forced to defend ourselves routinely, and on the rare occasions when we are, we find that a little foresight and common sense does more than any amount of martial arts skill. I had someone get road-ragey on me last week because I was driving "too slow" (I was stopped at a crosswalk with a short elderly pedestrian in front of my car). A smile, an apology and an explanation took care of the problem. Aikido wasn't needed, and honestly, if you neglect the skills of avoiding trouble and defusing conflict, aikido is not gonna save you.