Supports are actually handled differently in V5. There's no need for a separate checkbox to enable support material anymore. The software will just always add supports if there are supports present in the 3D view. This helps to resolve a common confusion of the old V4 software. So in short - if you want supports added in V5, just click the generate automatic supports icon in the bottom toolbar to add them to the 3D view.
Still is miissing in your answer, why % of infil is not possible increase/decrease with progress bar, as it was on V4 and why must used go to process setting.
That setting is on the Infill tab. With V5, there are additional infill percentages for the dynamic dense infill, as well as new support infill. There was far too many infill percentages to display them all as sliders, so they are no co-located on a single tab.