Another vote for velcro side saddles. I have the 5 round and 2 round ones Ares Gear used to make with the belt holders made under collabaration by Raven Concealment. My 590 A1 and Shockwave are set up the same way. 5 round loaded with OO buck on left side (another 5 round card on buttstock of 590), 2 round loaded with slugs on right just behind ejection port. I have 1 of each on the moduloader panels that I can throw on a belt. When a card on the receiver is empty just rip it off and swap with a full card. Same thing can be accomplished with other brands of cards and M16 mag pouches (including kydex ones) HSGI used to make one (still might) that was designed to work with their Taco pouches.
Only experience I have with fiber optic sights are the clip on ones made by Tru-Glo. It worked but, I went to XS ghost rings and never looked back. I eventually abandoned ghost rings for red dots. Now I have Trijicon SRO's mounted with Scalarworks SYNC mounts. It uses the RMR mounting pattern so RMR, SRO and some of the Holosun red dots plus anything else that uses the same pattern works on it.