You can do this 2 ways.
1. Dynamic menus, you can make custom menu items that execute macros in
EventGhost or girder.
2. You can use the OnScreenRemote STV to have basically many custom menu items on a single screen formatted to look like a remote control.
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The problem with channel +/- is SageTV's recording engine has no clue that you have changed the channel on the STB. I HIGHLY suggest you not do this but rather investigate the control method to see if you can speed it up. Really you need to change how you watch TV, live TV sucks and it is disabled in my house. Just setup your favorites well and watch what you want when you want to rather then when broadcast.
The PPV stuff should be easy to accomplish using either method.
For the PPV channels be sure to limit the number of tuners that have access to it so you can predict which tuner will be in use and which STB you will need to send the commands to. You can do this by making a lineup based on a close zipcode and only that lineup has the PPV channels enabled. Now you know PPV is only accessed by 1 tuner. Adjust that tuner to have the lowest priority so it will be the last one in use making PPV available for most of the time.
Now you would have to get EXEMultitunerplugin working (I am tring to do that now, without much luck

). You would need to build your macros so when EventGhost (or girder) sees the incoming channel change request it appends whatever commands are required to make the purchase. Probably somthing like a Right and an OK. This would allow Sage to schedule PPV shows without you having to kick them off from live.
I'm not a girder user so I have no clue of it's power but EventGhost allows you to add custom scripts into the GUI created macros. This would be required to differenciate the PPV channel changes (if %CHANNEL% is between 800 and 825) from normal channel changes that do not need the additional Right> command. Really though depending on your cable box you might be able to get by with adding a Right and a OK to the end of each channel change.