Could you please list all R/3 modules (FI, SD, PS, etc) supported by GuiXT? 
Are all transactions in each of these modules supported, in particular, 1.4? 
Which SD transactions, in particular  VAxx transactions, are supported?

GuiXT can be used in the same manner for all R/3 modules. This is in fact one of the big advantages of the GuiXT technology; it is not specific for a certain SAP application, but a generally applicable tool. So you learn to handle it for one module and can apply your knowledge to all others.
Order entry (VAxx transactions) is a very popular field for GuiXT, since this is an area in which many users are active, and where you can achieve very significant advantages with GuiXT.