Different systems have different top implementations, but in general it isn't very configurable. It's meant to show information about memory and CPU usage; disk space and logged-in users are not its job. Conversely, not showing lists of processes isn't its job either.
If you want a configurable system monitor, try conky. It's GUI-based. Or nagios's web-based dashboards.
If you want to display information of your choice in a terminal, you can use the
watch command to run a program every few seconds. Pass it a shell script that displays the information you want. For example:
my-favorite-statistics containing something like
For the CPU and memory part, you may want something nicer than
free might help for memory, or you can massage the output of