Why Holy Flash? You CAN use Holy Flash to get EMs, especially in combination with Miracle. Against AI3, I had much success with this combination, but I needed more Flashs and Miracles for a good EM rate. Arena is stronger. Sanctuaries are probably not strong enough to get your HP close to 100.
I would not use Holy Flash, here, not in Bronze (because of low
rewards).
If you still want to get EMs with this combo: -1 Holy Flash, +1 Miracle (and a few more pillars). A Miracle is much more useful than a Holy Flash. You need a 2 card combo for EM.
It doesn´t matter for your EM rate of your combo, if you have 2 copies of Holy Flash and 1 copy of Miracle, or 1 copy of Holy Flash and 2 copies of Miracle.
With 2 Miracle, you survive longer.More wins, absolute number of EMs increases.
You can also use air quanta generators to get more "dive". Then, I would use light pendulums with air mark for consistance of your deck, or air pendulums with light mark.
Arena players like Deflagration and Steal. Morning Glory is ok because of that, Long Sword, Gavel, Long Bow are other good choices.
The Mirror Shield is good, Fog Shield probably better. 40% miss chance means "up to 66 extra HP". Stacks with Miracle.