A small (256GB) SSD (whatever variety) is fairly cheap these days and makes an excellent OS/Program drive. Although you could get below 128GB on that drive, you would run out of wiggle room quickly, even when junctioning sample folders to another drive. The data reads from SSDs are phenomenal in comparison to a HDD.
Matching RAM sticks is optimal as mentioned above.
As far as dedicated GPU, DAWs are not 3D intensive, and only a few plugin makers make use of optimizing audio vs graphics anyway. A dedicated GPU won't buy as much throughput as the SSD "upgrade" mentioned above. If you ever get into 3D/video/graphics, then a dedicated GPU will help a lot.
As far as optimization, the standard disabling of core parking and not allowing USB connections (or the machine itself) to ever sleep are big. Also monitoring things that get loaded on boot (and disabling the garbage) is advised. LatencyMon and using msconfig and/or services are all useful in that. For some things it is easier to one-off those in these forums as you load the machine up (otherwise it will overwhelm you). Win 10 seems to require less tweaking than its predecessors.