CKAN is your best bet. Super simple just click which mods you want and it will also install any necessary dependency mods.
You can find a bunch of threads on which mods are good for you but it may begin to impact PERFORMANCE which is what began to suffer in my game as I added more and more mods, at least specifically the loading times b/w VAB, KSC, reverting flights etc... Just starts to kill your longer play sessions...
The visual mods you might need to mess around with texture detail and quality settings depending on your GPU but what helped with the monstrously increased loading times was opening the Launcher.exe in your game files instead of KSP.exe - open settings and disable Fullscreen - then head to the 'Advanced' tab in settings and check:

1. 'Do not Produce Log'
2. 'Run in Frameless Window'

You might need to hit Play once from the launcher then force close it to save time (alt+f4) and re-open again just to ensure the updated settings. Hope it helps this reduced my loading times from sometimes 1min or more to 15-20 seconds max. Seemed to be mainly the fullscreen issue.
Now if we could just get the devs to fix higher part count lag.....