I can't speak to the flash...yet. However, to answer your other questions; all fusilier regiments wore wings to denote their elite status along with white plumes (hackle) to denote their historical elite status as trusted troops to escort the train of artillery. Although escorting gun role faded away the fusiliers guarded their elite status and unique uniform distinctions. However, there was a company exception during the 'Great War' or Napoleonic period in which the light company sported green plumes. Yes, they generally did not wear bearskins in the field as they were expensive and so reserved for ceremonial duties in the UK. Although Haythornthwaite states that the 7th and 21st Fusiliers probably (at least by NCOs) wore bearskins at the start of the campaign and were soon replaced by shakos.
I have two pages of research notes on this topic and some of the references are Wellington's Army: The Uniforms of the British Soldier, 1812-1815, Plates by Charles Hamilton Smith and text by Philip J. Haythornthwaite, plate 29; Scarlet Coat: Uniforms, Flags and Equipment of the British in the War of 1812, Rene Chartrand, Service Publications, 2011, pp. 48, 49, 69; Uniforms of the Peninsular Wars 1807-1814, Philip Haythornthwaite & Michael Chappell, Plate 7, pp. 100-101. Military Dress of the Peninisular War 1808-1814, Martin Windrow & Gerry Embleton. Plate 64.