I can help with a few things..
If you liked what Ubuntu had to offer before Unity, just get the older desktop environments, such as GNOME2. XFCE is another good choice for more lightweight resource-usage. If you're after real lightweight yet beautiful DE's I recommend giving Enligtenment (E17) a look. I am using it with Ubuntu Studio and produces more efficient results than XFCE! It's also very customizable.
If your applications are slow from the very start, give "preload" a try
or get it from synaptic or the software center
sudo apt-get install preload
in case you can't get it up as with the terminal issue you had.
Preload basically lets your most frequent appplications start faster, hehe. Always helps with a good quick start on the things you want to do. Give Opera a try if Firefox is generally slow, as Opera I find is somewhat faster.. Konqueror is also another option which is in the repositories, ready to be installed if I recall correctly!