There are lots of ways to go with Caelum, due to their variety of strengths.

With only summons availiable to make into decent combatants, one common way is to focus on blood (since ID's make such great combatants).

Since Caelum is one of the few nations with access to a Natarajah, they are a common SC (especially since you already have Air and Water items covered for forging).

An important factor for using Caelum is getting a Wizard's Tower, if you plan on using alot of Iceclads (why wouldn't you?). So you can throw up towers quick and effectively every few provinces in order to churn them out. They gather easy and are easy to reinforce.