i dont know about pH calculations, buffer solutions, but i know a few things about writting equations.
first we have NaHCO3 (aq) + Pb(NO3)2 (aq) --> 2NaNO3 (aq) + Pb(HCO3)2 (s)
the net ionic equation is:
HCO3- (aq) + Pb2+ (aq) --> Pb(HCO3)2(s)
unless there are other reactants formed (not really familar with bicarbonates), the ionic equation will be the key.