There's a good short guidebook called "10 Classic Alpine Climbs of Japan". The author's blog is also pretty good.
(Caveat: alpinist, not BC'er)
You'll get some, but it is towards the end of the season and given the snowfall this year (low, generally) it might be on the shoddy end. I was on Tateyama/Tsurugi in early May last year and there were plenty of BC guys around there - it was baselayer weather, though, and pretty slushy by the end of the day.
Fuji would usually still be in, but again I'm just not sure this year - Jan was almost bare up there, and while there's been a decent dump in early Feb, it was getting warm again last week. Unless there's a decent fall again in March, I think May might be pretty barren.
Would recommend getting in touch with Damian at Hakuba Mountain Life for beta (https://www.facebook.com/mountainlifejp/?fref=ts on ) - tell him CJW put you his way :-)
If you fancy getting some routes in rather than skiing, then it's worth checking out Tony Grant's new ebook (http://www.amazon.com/Classic-Alpine-Climbs-Japan-Climb-ebook/dp/B01ARU5KR0) - a steal at only $5.99...