Better to play from a USB HDD on the Wii due to the slow SD port, USB sticks also have issues (or rather flash memory but there are fixes), though an SD card is used as part of the modding process, best option is ModMii that will download everything needed for the initial mod then just add the GC mod after and if needs be the loader of choice for me that was USB Loader GX, but there are plenty of others that one is just my personal choice
Best option given is possibly the PC port version as Dreamcast emulation is far from perfect and you still need a higher end computer to use that smoothly
Emulation wise your system falls under par for that generation of emulation PSX (With the correct settings/emulator) and under should be fine though, DS at a push maybe otherwise GBA and under for handhelds (e.g. PSX, Saturn, N64 emulation and under should work fine for you)
PS2 GameCube/Wii Dreamcast PSP ect are going to run badly for you though
You may find some N64 emulation is not great either on that machine but that is partly the emulators available as well as system specs
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