You should get on one of the web search pages and look up AIKIKAI HOMBO DOJO and YOSHINKAN HOMBO DOJO. They will answer most of the questions you have. All you need to do is explore the sites. Of course there are others but these will get you started.
You do not need to have any grasp of Japanese language but it is helpful. I recently returned to the US after a four year tour in Japan. Prior to that I had been stationed there for three years. You can get by in Japan with no Japanese language but again it is not the best way to get by. You can not get by in Japan without the appropriate finance though.
You do not have to have any experience in Aikido whatsoever, it is desirable though. Your financial support and living arrangements are up to you to work out before you finalize your trip.
You should also get onto the US Embassy web site and find out as much of the information you need to know to make your trip a successful venture. A good many travel to Japan and find themselves having to leave the country earlier than they intended because they hadn't prepared properly.