The interview and pre-departure process is probably a little nerve wracking for first-time expats since most communication will happen when there are developments on the Japanese side. They do, however, give fairly good information if one reads the materials provided. The hard part is managing expectations. Interac was pretty straight with me on the timeline they were working from once they decided when I should arrive. I still knew several months in advance when I would need to go and could make plans regarding my apartment and then-current employer.
As an Alternate Placement without an assigned placement on arrival in Japan, I went through the same training as the rest of my cohort and was kept in reserve. During that time, the staff of the branch I was temporarily assigned to helped me get settled as far as bank accounts, moving in papers, apartment setup, and the like went. (No one went with me to get a mobile phone but some of the other staff did give me some advice on contracts and a key vocabulary words so I could ask the carrier staff.)
My assignment came in mid-to-late December with a ticket on the Shinkansen to meet my MC and get a ride up into the mountains with one of our Japanese staff members. We only had enough daylight to go to a few of my schools for introductions and to get the keys for my apartment and car. Mr. H. made sure we had enough furnishings in my partial furnished flat to make sure I'd be fine until the weekend. Few things feel quite so lonely as looking outside your window at a town where you don't really know anyone and can only see about 50 feet out due to the snow (disclaimer: the San Francisco area doesn't get snow). If you can make it past that first night, it gets much better and quickly. Ms. I and some of the local ALTs met up with me over that weekend, helped me get my bearings, and how to contact folk in the area.
I'm in my early thirties and most of my ALT colleagues are in their twenties, so that does occasionally keep us separated. We do, however, tend to pass the word for an informal rendezvous or two each month. Due to the scheduling, our book club usually also has a chance to meet before the ongoing training sessions for our region. That being said, if you have a hobby or (school-appropriate) interest, you can find it helps as an ice breaker with some of the Japanese teachers, students and parents. (I was particularly flattered when the parents marked me as an honorary part of the baseball team after the end of the season.)
I'm currently living and working in a town that's very different (half the population, eight times the space) from my home town. There are some things where it's still largely the same, however, like transit time to major cities (trains are slower than highway buses or driving only due to the routes to my semi-rural town). There's not much for nightlife venues here but the town associations are good about having events every few weeks and most people are reasonably friendly.