WISE is essentially a giant archive to provide access to existing material on all kinds of anomalistic phenomena, much of it scanned from printed sources. There will be some new articles, but I understand these will depend largely on voluntary contributions.
The SPR will be smaller, and more tightly focused on psi-phenomena. The articles will be overviews of research in different areas, backed by case study summaries of key reports. Since we can pay writers we can put together a fairly homogenous resource quite quickly.
My personal view is that this sort of dedicated approach is needed to draw in readers who are unfamiliar with parapsychological topics, while WISE is ideal for those who wish to amplify their existing knowledge.
Some overlap will occur, but we have agreed to try to avoid pointless duplication as far as possible. Meanwhile we have left it open for some kind of collaboration further down the line.