If I am lucky enough to get a standard class Window seat on a Cross Country Voyager Advance ticket, will I get a plug point?
And what's the difference when booking between the Window and Window View option?
Yes you should do.
No need to be lucky; if you book with the XC or Trainsplit sites you can access a seat selector.
XC's site works for their own services only while Trainsplit works with any provider.
If you are making a longer journey, which on XC would be best value using multiple tickets, you may wish to consider selecting to recieve e-tickets as you can get all tickets for the journey in one single PDF which I find makes things a lot easier (especially for expenses and delay repay claims, where applicable).
The usual caveats apply (if you have the last ticket in the quota at that price tier, you won't be able to change it and of course reservations could be cancelled and the coach and/or train may not exist if disruption occurrs)