Set default text editor to pico (from vi)

$ which pico
Output:

/usr/bin/pico

Now setup a new text editor:
export EDITOR=/usr/bin/pico
OR
export EDITOR=pico

Add above line to ~/.bashrc file:
$ vi ~/.bashrc
Append text as follows:
export EDITOR=pico
Close and save the file. There is no no need to reboot system.

Also you can add alias if you want:
alias vi=/usr/bin/pico

setting quota for users:

apt-get install quota

apt-get install quota quotatool
$ /etc/init.d/quota start

/dev/sda1 / ext3 defaults,errors=remount-ro,usrquota,grpquota 0 1

touch /quota.user /quota.group
chmod 600 /aquota.*
mount -o remount /
quotacheck -avugm
quotaon -avug

To set the soft limits to 200Mb and the hard limit to 250Mb for a user called skx you would run:
quotatool -u skx -bq 200M -l '250 Mb' /home
repquota /home = view who uses space