The modpack adds many new mods, but the progression stays relatively similar to the one from “vanilla” Calamity. This page will tell you every bit of the progression that changed with the added mods and Calamity addons. If you want a progression guide for the Calamity mod itself, you can go to this page from the official Calamity mod wiki:
https://calamitymod.wiki.gg/wiki/Guide:Mod_progression
Or if you need help on the Terraria progression, check this page:
https://terraria.wiki.gg/wiki/Guide:Game_progression
<aside> 🚧 THE PROGRESSION GUIDE ISN’T FULL YET IT WILL BE WRITTEN SOON, for now you can check on individual wikis for changes
</aside>
You will spawn with the usual tools and weapons, the Starter Bag and “Overhaul the Bible”, which is a book that will show you most of the Calamity reworked weapons from Calamity Overhaul.
In the middle of the world you will see Living Tree. In the underground living tree, you will find many chests with some decent starter loot
Go to underground trips like usual to get some ores and loot. Remnants improves gem caves and also makes them more frequent, so you will easily be able to make a gem hook. Gold/Plat will only spawn below a certain point, you can take the depth below where the marble cave spawns as a reference. If you feel prepared and is searching for extra loot, you can try exploring the Pyramid, but be aware that the enemies will be quite tough for you at this stage of progression.
When building your base, remember of the many QoL tools given to you by the Quality of Terraria and LuiAFK mods
At this point you can explore some other structures like the Planetoids in space to get items like Heart Crystals to increase your health.
With the loot you gathered from your underground and overworld searches, you should get ready to fight your first bosses, you can begin making an arena near your base to fight the King Slime, then make another one in the Desert to fight Desert Scourge