Yes, this forum section is for both RadInput and RadInputManager.
Here is some information about your enquiries:
2) This is a known issue, which we are going to address, probably for the next service pack.
3) Adding a DatePickerInputSetting will practically duplicate the RadDatePickers + shared RadCalendar scenario with not much benefit, so I recommend you to use the latter approach. Alternatively, you can try using RadInputManager textboxes with a RadCalendar, similar to this demo:
4) Due to its specific behavior, RadMaskedTextBox requires several <input> elements on the client. Since RadInputManager always uses a single <input> element, a masked textbox scenario cannot be implemented.
5) We may consider enhancing the validation-related functionality in the future.
6) RadFormDecorator injects additional HTML elements in order to support rounded textbox corners in IE. This interferes with the autoexpand ability of the textboxes. You can set EnableRoundedCorners="false" and textboxes will expand as expected.
the Telerik team