I've never used smart previews it always seems like it takes a long time to generate, maybe it is because of using an underpowered laptop. Do smart previews take up much more HD space?
Also is there a difference in which video card I get? Should I get a gaming video card or anything special? I've heard to use the video card that is on the motherboard but it shares the regular RAM so i didn't know if reducing the RAM is going to be the best thing to do.
For photo editing a dedicated graphics card is not really needed, Lightroom 5.7 does not rely on the graphics processor, it relies on the cpu for processing. I would choose 16GB+ of RAM and use the on board graphics over a dedicated graphics card in a photo editing budget build. If you do get a dedicated graphics card or need one in the future a low level GeForce 7xx or 9xx based card will do.