I try to only s-mod in the most expensive hull mods. Hardened Shields and Reinforced Bulkheads are what I put on my Paragons, and s-modding them into the hull saves 60 OP!
As for why you should put hardened shields on your Paragon, with the right officer skills (shield modulation) you can get the shield flux/incoming damage stat down to 0.35. On a ship with over 2,000 flux dissipation (and with Front Shields or Stabilized Shields to reduce shield upkeep by 3-400 flux) this means you can absorb something like 6,000 (soft flux) DPS and you have the 15% hard flux dissipation under raised shields from officer skills, plus the fortress shield ability. So, in short, hardened shields makes an already tanky ship that much tankier.
I don't like heavy armor on my Paragon and go for reinforced bulkheads instead. Heavy Armor is good against big swarms of small ships but the things which have posed a dire threat to my Paragon in the past do enough damage to ignore the armor this ship would have from Heavy Armor (5x Tachyon Lance Radiant, Star Fortress with Tachyon Lances, enemy Dooms with Reaper torpedoes, etc.) or at least destroy the armor in one hit. Reinforced Bulkheads lets you take more armor-penetrating hits and keep firing.