The official website has some information about episode 1 as well as some screen caps (nothing spoiler, just character shots for the most part). Those images are also archived here. From the best I can tell, episode 1 will take place either during Rea’s and Nobuyuki’s wedding from OVA 3+1, or just after said wedding.
Finally, here’s a new promo image of the OVA 4 Tenchi harem. 😉
Well, I’m starting to get excited for this!