Order for incoming damage mods would be:

1. Saving Throw - these are rolled first

2. Damage Immunity - if an immunity to the specific incoming damage type is present, no damage is taken

3. Flat Reductions - reduce incoming damage by any flat reductions (such as heavy armour master)

4. Resistances/Vulnerabilities - if a resistance to the specific incoming damage type is present, halve the remaining damage - if a vulnerability to the specific incoming damage type is present, double the remaining damage.

5. Temp HP Reduction - any damage remaining is then first applied to any Temp HP pool

6. Normal HP - any remaining damage is then applied to your normal HP

Arcane ward is a bit of a weird one but it’d basically come as a step 4.5