SketchUp as a desktop application has so far not yet embraced tablet-specific features, eg. to work with “big” fingers (that cover the cursor), to rely less on mouse-hover events (for hints, tooltips) and to require less the keyboard (modifier keys, shortcuts). A lot of SketchUp’s UI is small, and the snapping aperture is also not configurable.
More and more Windows 8.1 devices come with “reasonable resolution” (aka. high dpi), which SketchUp does not fully support and makes touching small things even worse. (Now I can’t imagine anymore trading in my high-dpi convertible for something low-dpi, but then I also accept that SketchUp is not yet optimally usable.)
Buy a stylus (a simple, passive one is good enough). It lets you better see where you click, and makes it easier to snap lines to end points.
Keep an onscreen keyboard open for using modifier keys. Some keyboard programs are configurable, so you could for example save space and let it show only modifier keys, or a complete keyboard.
Context menu: If the OS does not by default use long touches as secondary click (right click), you can also set in accessibility options to “simulate” the secondary click by a long click (this setting is originally for one-button mice). It can also be convenient to use the context-menu key on the keyboard.
As for performance: Contrary to common belief, SketchUp can function very well on low powered machines (<1GB RAM) as well as with Intel graphics. Judgements about required hardware depend very much on what kind of work people do. If you work with big models with millions of faces, and don’t prioritize long battery life, go for a dedicated graphics card (like NVidia). Crashes come usually from poor quality drivers.
SketchUp uses one core, so if your tablet has two cores it should be fine. Instead of many cores go for a fast processor with a high clock speed (Intel i5, i7).