And a bit of advice. Basic Nagios can be a nightmare. There is little guidance what goes in what config file and if you’re doing this more less on your own you will likely create an original system that won’t comply with “best practices” … So, for example you’re asking about hosts, but did you know about Hostgroups? Do you know how to create profiles?
My strong recommendation is to instead deploy any of a number of really great products built on Nagios or close alternatives to Nagios. Usually a web interface, you’ll build a much better monitoring system.
A few (by no means complete and as of today) suggestions, except for the last mostly if not completely free
NagiosXI - By the core maintainers of Nagios, free for something like less than 20 monitored nodes
Zabbix - Completely re-built, but at the User Level similar architecture (plus more)