What are the g-block's predicted properties?
First of all, from the perspective of chemistry, it is the group (column) that matters more than the period (row), and subshells act at the period level.  Second, the elements beyond the actinides have virtually no significant chemical research owing to their extreme radioactivity.  So there may not be many predicted properties for the g-block beyond the simplistic theoretical assumptions about groups, which are much less relevant for a hyper transitional period like the g-block.

As for you question about potential stability, Glenn Seaborg made some predictions here, which you can read that this Wikipedia page: Island of Stability.  In general, though, these elements are not predicted to be stable.