how to know what drivers are installed and what aren't?

Use your service tag in the Dell Drivers and Downloads Page. (Not on the forum)

Go to the page, at the top select change product then input your service tag, it should remove the ones that don't apply to you're system.

Actually in my case it isn't doing it, it used to for my laptop. In general try installing drivers you are unsure of. If the hardware isn't found on you're system then they will fail to install. Again with the USB 3.0 ones try installing both, it may be an either or however it may also be 2 complementary drivers.

And to know whether you installed the driver is another case. When you download the driver it will be called Rxxxxxx where x is a series of numbers. 

If you look in C:\Dell or C:\Drivers\Dell and find a folder with Rxxxxxx (the same number) then you know you have attempted to install it and it is at least extracted.

Sometimes the installers don't autorun however. You should double click the .exe file

Get something like this click continue. After that it should finish and then an installer should come up saying do you want to install etc. If this installer does not come up you will need to go to C:\Dell\Drivers\Rxxxxxx and click any setup.exe

I don't know why the service tag is no longer narrowing down the driver set.

You confused your question a little. The setup won't fail if you don't have the driver installed. Otherwise no-one could install any driver they need ever.

The setup will fail if you are trying to install a driver for hardware that you don't have.

For example on my system I have an ATI graphics card. If I try to install the driver for a nVidea graphics card it will come up with some error and nothing will be installed.

The 2 USB 3.0 ones should work fine I think.