falconsoft not really the right place for these questions as this is a thread on a third party graphics pack.... but anyway:
2. In app purchases are dependent on what platform you are targeting, you will need to find the appropriate plugin for your platform. Clay.io, AppMobi, CocoonJS, etc... all have plugins here it just depends on how much the particular plugin has been developed and which features are supported. Scirra does not make the third party plugins.
3. You can create your own onscreen keyboard just fine. There are also plugins for text boxes, etc... so that browsers will treat them as any other text box and present you with the onscreen keyboard natively. Otherwise you can create your own and assign actions to each button like simulate key press "X".
6. This is 2D only, no 3D support here as it uses the HTML 5 canvas object for all rendering. You can visually create your levels. Again try the free version for awhile before deciding to buy. What you get in the free version is what you get in the licensed version with the exception of families, containers, and exporting to different platforms. All this can be found on the licensing description in the manual.
I highly recommend trying the free version, going through tutorials and reading the manual. That will answer pretty much every question you asked in much better detail than I can.
Hope this helps.