I completed the Legendary WRE campaign with Latin Christianity. That said, Roman paganism gives a +2 bonus to sanitation, which cannot be ignored. Religious affinity provides a bonus to diplomacy, so it definitely has its uses.

There are different benefits to Roman Paganism and Latin Christianity. Latin Christianity spreads very well into neighboring provinces, to the point where many will swap to the faith during the course of a campaign.

Obviously, there are exceptions to this, but I will go into that later.

Climate change will reduce regional fertility, so you need as much food as possible to not only keep yourself food positive, but to also boost faction-wide growth and replenishment.

Even if your overall food is positive, any province that doesn’t generate surplus food is going to suffer from a base -1 public order and -25% wealth generated (Depending on how much food you’re in the negative, that public order penalty increases).

Each province should to be food positive.

However, Roman troops are some of the best in the game, which justifies the cost.

Your troops are expensive. You will probably recruit very few units in the first 20 turns, if any at all.

You can research technology later that will reduce global reduction, as well as specialize your governors to reduce corruption also. The easiest way to reduce corruption is to lose territory. Corruption is related to how much income you generate the more corruption you have, the less money you get. The easiest way to go about this is to turtle up in a defensive position, build infrastructure, research technology, and build strong armies before expanding outward. So what do you do in this situation? The goal is to survive again the odds, defeat your enemies and the Huns, and recapture/conquer land.

Public Order is dropping across every province, due to religion, events, and immigration.

Corruption is in the high 70s your empire is vast but generates very little money per turn.

On top of that, your enemies are either neighboring you or traveling through your lands. Everyone hates you due to the fact you’re a “Great Empire”.

You’re at war with a few factions, with more joining before the you reach chapter two.

This campaign is the first “legendary” start difficulty campaign in the Total War franchise, and for good reason: This is the initial section of the Western Roman Empire guide. Western Roman Empire Guide – Part 1 – Important Campaign Basics

How to win rome total war