No, only gambatte-sr https://github.com/pokemon-speedrunning/gambatte-speedrun/releases or gse https://github.com/CasualPokePlayer/GSE/releases/tag/v0.3 are allowed w/ a gbc bios.
No, sorry - 3DS itself does not accurately emulate red/blue anyway so it is instead a category extension https://www.speedrun.com/pkmnrbext?h=3dsvc-any-glitchless&x=5dwzp9nd-ql6yr9w8.ln834rjl but even to be eligible for this leaderboard you would need to be playing on original unchanged hardware on a 2DS or 3DS. Unfortunately, the games are not even available for purchase anymore on 3ds so i don't think there is much of a future prospect for gen 1 and 2 having active leaderboards for 3ds - this is just my opinion, and ofc anyone who wants to speedrun for fun on any platform should totally just do that cause why not :)
For hardware, I would suggest a Gamecube that can run the Game Boy Interface software, or a SNES and a Super Game Boy 2 for it.
Though SGB2 is allowed, rng manips will not work properly on SGB2. If you have a PC, emulator is a great option. If you prefer console, then yea you want a Gamecube with the Game Boy Player attachment - then you need to either setup Game Boy Interface software for the best quality output (GBI-SR) or you need the official disc (GBP). You can typically find a gamecube with the GBP attachment w/ no disc included and then follow this guide to setup GBI-SR https://docs.google.com/document/d/1_L4Fq1oTLlR2rNgW0jC3hddr0uFb3ezNIQQohE4uTwc/edit?usp=sharing
