1. You can remove this arrow adding the following code to the Custom CSS area in Theme Settings

.woodmart-back-btn {
	display: none!important;
}

Sorry, but there are not options for different font types for particular categories.

2. Recommended size for page heading image in your case is 1900×300. And there is no such recommendation for your banner Visual Composer elements since it depends on your layout.

3. You can edit your sidebar widgets in Appearance -> Widgets.

Regards