Between RAM and SSD, SSD will give far more noticeable difference in form of considerably faster loading times. And that is not only for games but for everything else too, e.g system boot up and shut down times, file read times etc.
Good SSD to go for is Samsung 850 Evo. 250GB in size the most common size used as an OS drive with room for games,
pcpp:
https://pcpartpicker.com/product/3kL7YJ/samsung-internal-hard-drive-mz75e250bam
My Haswell build (full specs with pics in my sig) also has 850 Evo as an OS drive but mine is 500GB in size.
Though, for gaming aspect, biggest jump in performance would be GPU. While GTX 1050 Ti can do medium settings @ 1080p, GTX 1060 can do ultra settings @ 1080p with solid 60+ FPS. But the downside is that the GPU prices are currently through the roof.
Additional RAM helps too but won't give as noticeable difference in gaming as SSD would give. Extra RAM is handy if you play games that require 6+ GB of RAM or when you have lot of bloatware hogging your 8GB of RAM, leaving less for the game.
With your build, i'd go with SSD and make it out of the OS drive. While keep gaming on ultra@720p or medium@1080p.
As far as PC case goes, that's completely a personal choice. Fancy gaming themed case won't give any performance but it gives plenty of eyecandy. Without knowing your taste regarding PC cases, i can't suggest you which one to look for (e.g plain, fancy, acrylic side panel, TG side panel, small, big etc).
I, personally, like my PC to look fancy and i love bigger cases. That's why my Skylake and Haswell builds also sit in a full-tower ATX cases and i've created light show inside my PCs with addressable LEDs. Full specs with pics in my sig.