In a galvanic cell,do charges accumulate on electrodes 1st (then redox occur) which produce E in the wire when we connect between electrodes?
You can imagine the cell electrodes as capacitors, that are charged by chemical way. 

But the capacitance of these capacitors 

$$C=\frac {\mathrm{d}q}{\mathrm{d}E}$$ 

is very small, so does the accumulated charge $q$.

The charge loses due pushing electrons  through the wires of a closed circuit are balanced by simultaneous recharging by ongoing redox reactions. 

If we consider the zinc electrode of the Daniell cell, the reaction :

$$\ce{ Zn -&gt; Zn^2+ + 2 e-}$$

is charging the electrode negatively, while the opposite reaction:

$$\ce{  Zn^2+ + 2 e- -&gt; Zn}$$

is charging the electrode positively.

The electrode gains such a potential, where both reactions are ongoing at the same rate.