That definitely won't be the case. Even the lowest spec'd Windows Phones run butter smooth, unlike Android.
It is a shame you don't like the 820 since the specs seem to match exactly what you are looking for - but preference always plays a large part in phones so it is understandable. Then again, since you read a lot you probably want to get the 8S/8X LCD over the 820's AMOLED, as LCD is better with black text on white background than AMOLED which struggles with all-white backgrounds.
The usable space will probably only be in the 2.5gb-3gb range after you account for the size of the OS and apps that come with the phone. That remaining space must hold all of your apps; most apps are 25mb-250mb in size, so that is your call if it is enough space; for a user that isn't into games much it would probably be enough. Remember, though, for music and movies you can always use the microSD slot to hold media. You can't use it to hold apps, but you can at least offload all media to a 8gb MicroSD card and use the phone's 4gb for pure apps and OS.
Of course, I can't answer that for you. It really depends if you can deal with a slightly smaller screen size. I've used 3.8" for over 1.5 years and it has been fine - then again, I do want at least 4.3" on my next phone (preferably 4.5") as I'd prefer to have to do less zooming and see videos bigger... you will have to do a bit more panning and zooming but a smaller screen certainly is doable. So, your call - is the significant extra cost of the 8X worth the 0.3" larger screen, higher resolution (8X:341ppi vs 8S:224ppi), and 12gb additional storage? That 8X may cost a lot more, but you will get bigger size, clearer text, wider game selection, and more storage space for a phone you are probably going to keep for a long time - might it be worth saving up for? Maybe not, boil it down to money vs inches/res/GB and there is your answer on whether the 8S is good enough or whether you should save up for something more
That is hugely personal preference, but I would definitely go blue for myself... or High Rise Gray/Yellow.