2) If you go to Japan, then train in an MMA school. Don't "overthink" your options. Analysis is paralysis.
3) Aikido takes longer to become proficient in than you have time for if you're dabbling or cross-training in other styles. If you're going to take up Aikido, then you need to be totally dedicated to Aikido for a solid 5 years. Ditto for Aikijujutsu or any other traditional Japanese martial art. Did I mention how expensive most martial arts schools are for just one system?
1. Sure you could do it. But it is not necessary. It can lead to confusing and stunt your growth as a martial artist. That is not to say that it can't be done. You have named aikido, hapkido, judo, and bjj. All of them are good, but may limit what you will learn since they are offspring of jujutsu but have had many of the techniques removed.
If your goal is self defense and you are in a good school you should stay were you are. Jujutsu was designed for 2 things and that is to maim or kill. That is self defense. But if you look at arts like bjj it is meant for winning a sporting competition. The objective is to win not self defense or life preservation. Judo was taken from jujutsu and so was aikido. Judo in most places today is taught as a sport, but it origin is budo. A few schools still teach judo as life preservation, but they can be difficult to find. Aikido is also from jujutsu, but is meant for a peaceful way to resolve a conflict. It can be used to maim or kill as the user always have the choice to do either. But the hope is that you will choose to to injure or kill. Hapkido is similar to aikido. In both of these in most cases you won't cover as much of ne waza as you would in jujutsu. BJJ is sport today. It focus is to get you on the ground and control you and make you submit in order to win. That is fine in self defense, but in today's society that would not be too smart everyday. There is a good chance the attacker has a weapon or there will be multiple attackers. In a good jujutsu school you will learn some good tactics on what to do if there are multiple attackers or if there is a weapon. Very seldom will you learn that in most bjj schools.
I want to add please don't stop at getting your black belt in jujutsu. Many people see a black belt as the end of their journey as a martial artist. But this is far from the truth. A1st Dan is still basically a beginner. It is at this point you have just covered the basics. Now the real learning begins. Not that you have learned prior, but you will learn to put everything together. You will get better at and learn more how to use your strikes as a distraction and how to end the threat quickly. You will learn how to disarm people with knives, guns, sticks, bats, etc. You may even learn how to defend against multiple attackers some armed and some are not.
2. I can't help you with the good jujitsu school in Japan. If you can find one it would be great to train there while you attend school. There would be much to gain by doing this. You might start by asking your instructor. Often some instructors have a resource in Japan. They can recommend you and tell you how to get accepted into a good school and who to talk to about training.
3. Aikido proves nothing to jujutsu and neither does any of art prove anything to any other art. What matters is what you as an individual do in your art and training. No art is better than another. Most ave some similarities. They may structure the classes differently. But no matter what it is still left to the instructor on what is taught and how it is taught. Next it is left to the student on home time and effort they put in. The student is responsible for how well they learn to apply what is being taught. No matter how hard some try to say this art is better than another or that you need to cross train to be more well rounded all of those things are fallacy. The variables that will determine any outcome are the quality of instruction and the quality in the persons using what they were taught. Those individuals are the variables to the equation. No 2 students are equal and no 3 instructors are equal.
No matter what you choose to do remember it starts with having a good instructor and you being the best student that you can be. There are no short cut to real training.
My friend once you do BJJ you'll forget any of the other Ju Jutsu styles. If you do decide you still want to train Japanese Ju Jutsu, cross training BJJ aswell won't hurt at all.
Also don't be so fast to write off Judo, the founder Jigaro Kano created it as a safe way to practise Ju Jutsu in real time. The Tokyo Police put on a tournament to see which Ju Jutsu style was the best and Kodakan Judo pretty much dominated with the exception of a few Kosen Ryu Ju Justu guys. I put a YouTube link for you. Imagine they were fighting on the concrete and you'll have your self defence question.
I wish I knew about Judo & BJJ when I was your age.
I'll start off with the question i am most interested in the answer to.
1) Is it worthwhile to do multiple forms of Jujutsu? For example, I'm currently a Brown Belt in Traditional Jujutsu at a pretty good school. I'm thinking Aikido, Judo and BJJ (I think Hapkido would be very good aswell because, if I recall correctly, it has more focus on strikes than all other forms). I know I can go to Aikido, Judo and BJJ quickly if I wanted to. I want to get a black belt in my current school AT LEAST before going to another style, but is it very beneficial (I think Judo would be the least beneficial in terms of self defense, but I'll probably do that as it's a sport so I can truly practice what I've got) ?
2) Know of any very high quality Jujutsu dojos in Japan? I plan to pursue Jujutsu very strongly, as I'm still only 15. (It's not a McDojo, I've been doing it since I was 6). I am planning to go to Japan in order to study at a very good acadamy/school/dojo, but do you guys know of any? Does it work like that, are there any particularly good schools?
3) What does Aikido prove to Jujutsu in terms of self defense? I know they are a good pairing, but why so?
When I say Jujtsu, I mean Jujutsu and Aikijujutsu because I consider them to be very similar.
