Games installed, but not really

yes a ssd drive help improve the loading times a lot

The downside of SSDs is that if you install and uninstall a lot they are more likely to break

There is an improvement when using SSD drives especially in games where the load times are already long (GTA5, The Witcher 3 etc). If I were buying an external drive, I would go SSD over a normal external hard drive not just for this generation but to ensure
it lasts well into the next gen. There are loads of tests carried out by external organisations like Digital Foundry that show benefits of SSD drives.

With installed games, you would still need the disc if it was a physical purchase or the account you used to purchase the game to play whatever was on the SSD.

Sure it will work as long as you have the disc in the tray. A SSD has faster loading times than a normal HDD. The usage without the disc works only if you buy the digital version of the game. Hope that helps.

you are able to use SSDs - yes, I am still on a traditional external HDD, but various people as i've seen in youtube see a better performance by a few seconds using an external SSD