How does the maximum current of solar cells combine in series?
When connected in series, the maximum current is as high as that of the weakest link, so yes, 4A. The voltage will be the sum of all cells, so 1V.

When connected in parallel, the maximum current is the sum of all cells, 12A in this case. If you do this, you should only connect cells of the same voltage in parallel, otherwise you get unwanted current flows.