i'm an fz5 user so i'll help out. the flash i'm using is an emoblitz ds328az flash, which you can get from AP SLS. Err, it acts as a slave flash in a sense it detects the first instance of the on-board flash before it fires off.
Metering wise i'm not sure.
it has 3 modes, N, S1, S2. N for normal hotshoe contact, S1 for 1 burst of flash while S2 for 2 bursts of flash[this i read from the manual].
As far as the shutter speed is concerned i agree it is limited. Based on having using it countless times on my fz5 i can safely say the range is from 1/60 to about 1/200. Anything above that i don't think you can trigger it.
You might need a flash diffuser cap like stofen omnibounce or what Hexlord suggested to me was to get a $15 suntax diffuser cap from AP Sls, works like an omnibounce.
Hope that helps
P.s. After viewing the optical slave hotshoe unit on Tchuanye's i decided to try and get one to see if i can experiment a workaround for the limited flash range. Will update you once i get it.
the flash itself.
the flash with my, often laughed at but works most of the time flash diffuser, something like LS.