You seem to be asking how to install a more fully featured user interface on Lubuntu.

Lubuntu is Ubuntu with the LXDE desktop environment instead of GNOME/Unity. In some ways we talk about it as a separate, derivative distribution, but really, it's just Ubuntu with different packages installed.

You may want to try the Xfce desktop environment, which is lighter-weight than GNOME (whether GNOME with Unity or GNOME with GNOME Shell). Xfce uses more resources than LXDE, but you may find it runs well on your machine. I recommend trying it. Unless you're very low on disk space, installing it shouldn't cause any problems, and you can always decide not to use it if you don't like it.

The best way to install Xfce on Ubuntu (or Lubuntu, or any other derivative) is usually to install the xubuntu-desktop package.

You can do that in the Lubuntu Software Center (which you may or may not have, depending on what version of Lubuntu you installed), or the Synaptic package manager (which you should have if you don't have a Software Center). Or run this command in an LXTerminal (Ctrl+Alt+T):

sudo apt-get update && sudo apt-get install xubuntu-desktop

Then log out, and on the login screen, you can select Xubuntu as your session type.

For information on using Xfce in Ubuntu, see the Xubuntu website.

Yes. If you don’t install many apps, 8 GB is enough for Lubuntu. Conseidering that settings and apps user data are stored under home partition, Lubuntu File System takes 2-3 GB at the beginning; you add extra 5 GB for apps and a room for breathing. (Once I myself installed Lubuntu on a 80 GB harddisk, made a 10-GB partition for File System.)

In the case of 1 GB RAM you won’t need much than 1 GB SWAP – Lubuntu itself takes less than 100 MB on startup.