If you aren't playing with a romhack, I'd suggest Pokemon Emerald instead of Firered. But you may want to look into some simple romhacks that will add QoL from later pokemon games (along with fairy type, etc.), and that unlock all pokemon so that you can actually obtain every single one without needing to trade.

As for recs:

Any GBA Fire Emblem game. The JP only one, Binding Blade, has a full English fan translation patch that you can apply to the rom. I've never played Sacred Stones, but Binding Blade is better for gameplay, Blazing Blade (or just "Fire Emblem" in the English market) has better story/characters. If you're already a Fire Emblem fan, then Thracia (on SNES) is one of the best games in the series; just make sure to use a guide (there's a spoiler free one out there somewhere) because the game has some really bad design that punishes the player for not knowing things (like needing a certain amount of keys before a certain level).

Megaman series on NES. Megaman 2 is one of the best games of all time imho. The others are fun, but they do get repetitive.

Super Mario World. Best platformer of its time, and probably one of the best of all time. You can play SNES version, but I think Super Mario Advance 3 (?) on GBA also has it (I think this one has the JP levels too?).

Double Dragon (on NES) is a fun beat-em-up for the time.

Frogger (on various systems) was a fun game for its time.

I'd be remiss to not recommend The Legend of Zelda Ocarina of Time. I'm not a huge Zelda fan and even I found this to be a great game. At the time, it was simply unparalleled. Even now, it holds up really well, although its open world looks sad to anyone that's only every known modern games. I believe it's been decompiled, so there might be a PC version out there somewhere. There is the 3DS version which updates the graphics and fixes some annoyances and improves gameplay, whereas the N64 version has romhacks and (presumably) texture packs. Actually, there's a Gamecube version too if you want to emulate it on there.

On PS1, the Darkstalkers series is fun if you like Fighting games.

NES: 1942, Battletoads (also on other systems)

SNES: Aladdin

GBC/A: The Legend of Zelda Oracle of Seasons (and/or Ages)

N64: The Legend of Zelda Majora's Mask, Mario Kart 64, Mario Party 3, Donkey Kong 64, 1080 Snowboarding

Make sure you've looked into texture packs for the 3D consoles. They can make a huge difference in terms of emulating the game on modern screens.

If playing SSX, unless you have a reason to prefer PS1, I highly suggest just playing Gamecube or PS2 versions of either SSX Tricky or SSX 3 (depending on which on you prefer). SSX Tricky is insanely fun.