You have slight tearing issues. This either from outdated graphics drivers, or an overheating graphics card. If you install the latest drivers and it doesn't clear up, then you'll be looking at a new graphics card

Check out www.curse-gaming.com for addons. I would install whatever addons you want, it may be overwhelming at first, but after a while you'll begin to see which ones you really need and which ones you don't. Most of the top 10 mods there are must downloads imo.