My view on shield is this...
In the long term, minimal shields are better

Rationale:

Using a Heavy Obviator as an example, adding 52 deck each mod would add 26 to your damage cap and 559 shield, that is 21.5 'hit points' for each 1 point increase in cap. So if your ship takes more than 21.5 hits to kill at damage cap, it will make you easier to kill, and if it takes less than 21.5 hits to kill at damage cap, it will make you harder to kill.

For your ship as it is right now, you have 18355 points of combined hull + shield and a damage cap of 1214, so 15-16 hits (15.12) to kill at damage cap. Adding decks to have 5 heavy obviator mods would give you 21150 points of combined hull + shield and a damage cap of 1344, so still 15-16 hits (15.74) to kill at damage cap. It is slighly better but hardly noticable.
At some point in the long term you will stop adding decks, but you will keep getting brackets and x-cells.
You will get to a point where your hull + shields have both grown past having 21.5 hits to kill at damage cap, having added shields will start to be a detriment. Small at first, but as time goes and your ship gets harder to kill, the impact will grow.

IMHO a small gain now for a long term detriment is not worth it.

I intend to only have Aegis Capacitors (+5% shield each will have a larger impact with more x-cells) and the Mega-Coil Repulsors (for the +5% NPC def) and no other shield mods. I may even decide to not install the Mega-Coils as I get my def higher by using helmsmen or more def mods.

Can always just re arrange for the repulsors as needed.

Yeah, its only 60 deck for all 3 so it is easy to fix down the line

Alright thanks for the advice, so shields are a no go then.

I've used Thundebolta's calculator and if I equipped all 5 obviators, I would get an extra 2, yes 2! extra hits.