1. The top bar is probably part of the Rainmeter widget: [link] The right side is definitely from Rainmeter, so the left is probably just a custom set of transparent icons he made for various things.
2. The font would be changed by the Visual Style (VS) theme: [link] You'll need to install a UXPatcher for your specific OS version to install custom themes, or use a program like WindowBlinds, depending on the type of VS being provided.
3. The drive icons are here: [link] They were probably changed with something like IconPackager. The shortcut pane on the left is also part of the VS theme, as shown in the sample preview.
4. Yes, it is a Rainmeter widget. Also shown in the sample preview.