The Brocho of Shehecheyanu is not recited on the Daled Minim.
One may prepare for Shabbos on Friday as long as at least a Kezayis of the cooked Eruv Tavshilin item remains edible and accessible. Otherwise, one should discuss his options with a Rov (even if the baked item remains). In any case, one may complete all stages of preparation for food that one already began preparing whilst the Eruv Tavshilin was present.
Preparing for Shabbos is allowed only if there is still enough time for guests to theoretically arrive and partake of the prepared items before Shabbos begins. Therefore, the Cholent should be fully cooked some time before Shabbos.
The Eruv Tavshilin is effective only for preparations involving food and food utensils, or other meal-related matters such as lighting candles. The Eruv is not effective for non-meal preparations such as rolling the Sefer Torah or performing an Eruv Chatzeiros or Eruv Techumin.
One may theoretically eat the Eruv Tavshilin once the Shabbos preparations are complete. However, it is preferable not to eat it until Shabbos.
