Is it forbidden for me to expand part of the shop onto the sidewalk and the street, following the example of neighboring shops, and is it permissible for me to display goods on this part if that is forbidden?

It is not permissible to take a piece of the pavement and build upon it, annexing it to a shop, because this constitutes usurping land unjustly and without right. The Prophet (peace be upon him) said: "Whoever takes a piece of land unjustly, he will be swallowed up by it on the Day of Resurrection down to seven earths." As for displaying goods on the pavement only during selling hours, this is permissible if it is customary and does not harm passersby or narrow their path. Streets and roadways are shared by Muslims, and it is permissible to benefit from them for buying and selling, provided it does not harm passersby.