The G-Pen is overpriced for what is it/does. I highly suggest checking out the portable vape section here on FC for alternatives. Don't be afraid to ask questions, but try to keep to device specific and make sure to read through the threads to avoid asking questions which have already been answered.
Just regular eliquid? Like ecig liquid? ego battery and a ce4 or a vivi nova mini or something along those lines would work better. Lots of good info out there but this forum mostly focuses on herbal vapes...
What do you want to vape? If it's e-liquid, here's a good forum for you - http://www.e-cigarette-forum.com/forum/
If you want to vape a mj concentrate I'd quit thinking in terms of e-cigs. For good quality you need something bigger, and designed for mj use, not a converted e-cig.
You don't vape glycerin. You use it to vape nicotine juice, the same as propylene glycol. And no, you can't just buy a vape that will do concentrates or e-cig juice, as if they have the same vaping requirements. You've got some reading to do.I'm just looking for some pen had both capability for concentrates and glycerin