Just to correct some information:
It’s Pokemon Bank (transfers pokemon Gen 5 and up) that will be at its end of service, and will no longer be compatible with Pokémon Home.
At minimum, you would need a GBA-compatible DS (for GBA to DS), a 3DS (for Gen 5 and up), a single switch and a Home subscription to get everything into home.
You also at least need a Gen 4 game and BW2 in its Post Game to transfer beyond the DS era.
If you have some games already, great. If you can get a couple more in a fast time, also great.
You won’t need two 3DS consoles to transfer Pokemon! The DS and single 3DS should be enough to transfer Pokemon from Gen 4 to Gen 5!
I specifically urge you to get either Black 2 or White 2, as they’re the games that introduced PokeTransport in order to put Pokémon into Bank. Note again, you have to beat the game and enter post game.
You technically CAN get additional games (gens 6-7), but it’s not necessary as Home has a way to connect to Bank until the shut down, as long as you have Bank on the 3DS (and a subscription on Home).
Bank functions similarly to Home in holding Pokemon from different games, as It’s capatible from Gen 5-7.