This last part is great advice.
When you are starting to fill out your fly inventory, you might do better to focus on buying for form and function rather then specific flies. That way you start with a box that is built for multiple species. Impressionistic flies often work better than super realistic flies because they can represent multiple types of bait. For redfish, (and flats fishing in general except top water) I like to start with a fly that rides hook point up. Next I consider size, weight, movement, color and sound in about that order. So a fly like a 2.5 inch tan Clouser has all those attributes except sound. It is a fly that every fisherman should carry a few of. It is generally considered a baitfish imitation but it can catch a lot of fish when they are feeding on shrimp.
My personal favorite impressionistic fly is a jig hook flash tail whistler. It has all the characteristics of the afore mentioned Clouser, but it also pushes a lot of water which fish feel (like sound). It can represent everything. Bait fish, shrimp and crabs. It's my go to for everything, but especially redfish. Carry it in several sizes, weights and colors and you are good to go subsurface in almost every situation. I tie my own, but I have seen them on several online sites, although the jig hook version is less common.
Add a few good top water flies, and you are covered for most species at a low cost. After that, you can fill in with flies that look good to you for specific situations.
https://midcurrent.com/flies/hooks-the-jig-is-up/