So is there no official support from the company on this forum? I want to buy this product but it appears there's no classic theme I can use on Windows 8.1 if I do?
as this has been answered one month ago, i am surprised you are not using Windows Classic already.
no, you don't need WindowBlinds. no, you don't need a custom visual style. both these options will not help you. for either of them there is a possibility somebody might one day create a skin/visual style that looks like Windows Classic. i wouldn't bet any money on that. you can also use both to create your own skin/visual style. this is not rocket science, but it is pretty time consuming, especially if you never did something like it before.
it would be much easier if you just use one of the High Contrast themes that come with Windows 8. then change the colors to your own preference. takes less than five minutes and you're done.
if the large close button irritates you, do a Google search for "close button resizer Windows 8". shouldn't take longer than another five minutes.