First off, welcome!  :)

Quote - ... It's actually on a Microsoft Surface Pro.

A tablet is not an effective tool for creating 3D art.

• It lacks the video processing power required to maintain smooth performance in the Preview window as you add content to your scenes.
• It lacks the drive space required to store your content as you build your collection.
• It lacks the RAM and CPU power required to quickly render your final images.

Bottom line, you're going to quickly find the Surface woefully inadequate for your needs as a burgeoning artist.

Quote - Rendering takes time, of course, but I don't have much of a comparison for how long renders typically take in Poser, as I'm new to it. But, after installing Anastasia, and rendering one of the setups that is included with it (model, pose, lights, backdrop), it renders in probably ~2 minutes.

That render time will increase sharply when working with more complex scenes.

Quote - The tablet hasn't had problems with much of anything I've thrown at it. I've loaded Mass Effect 2, Bulletstorm, and a couple other games, and it runs them well.

Video games use visual effects that are baked in to the software.  There's no raw processing power required to render them.