If you have an iPad, an inexpensive way to get started may be Splashtop’s Splashtop 2 app (currently $9.99), which appears to do a credible job of letting one remote view/control a Windows 8 PC using the Modern (Metro) UI gestures. It might even be worth a try on an iPhone having a Retina display. Be aware that additional cost (in-app subscription purchase) is involved in order to use it remotely over the Internet (away from the LAN/WIFI that the Windows 8 system being controlled is connected to).
itunes.apple.com/us/app/splasht … 09315?mt=8
They have an older Win8 Metro Testbed app, but I’d be cautious, as presumably has been deprecated in favor of the above.
itunes.apple.com/us/app/win8-me … 78988?mt=8
You might also check out their Gesture Touchpad for Win8, which enables an iPhone (and thus presumably an iPad) to function as a touchpad for Windows 8. $2.99 I don’t know how faithful/native it is to Windows 8 Metro UI gestures… but pretty low risk, in terms of cost.
itunes.apple.com/us/app/gesture … 40812?mt=8
There are other iOS apps for iPad/iPhone remote view/control of Windows 8 PCs… possibly with some degree of Metro UI gesture support/compatability… Ignition, TeamViewer, … I think you can try the TeamViewer for free.
Best ultimate, but costly, bet is presumably an actual Windows 8 tablet. If in doubt, the reference is presumably Microsoft’s own Surface Pro (not Surface, which runs RT).
Windows 8 laptops with touch sensitive screens might be an option… and possibly cheaper than a Windows 8 tablet.
An external touch sensitive display monitor might be an option.
As far as an external touch pad/track for Windows 8, some possibilities, which I have absolutely no experience with or opinion about, might or might not include the following:
microsoft.com/hardware/en-us … technology
Apple Magic Trackpad on Windows via Magic Tools
Some unrelated but possibly useful tools for making the Windows 8 environment more tolerable during development, from Stardock. The upcoming 8.1 upgrade may lessen or remove the need for these…
Start8 (brings back Start button, make traditional Windows GUI more readily accessible/defaultable)
ModernMix (lets you launch Modern (Metro) apps in their own windows, as opposed to full screen, so they don’t take over the entire screen… and so can run such in the traditional Windows GUI mode