Yeah, no problem.
At least Nintendo had their "games can't be bigger than 40 megs" policy so even if you would only buy the biggest WiiWare games you would be able to get at least 8 of them before running out of space
The game sizes are shown as "blocks" on the Wii and I think the biggest WiiWare games take up somewhere between 300-400 blocks.
The smallest VC games are somewhere between 10-20 blocks.
EDIT:
Oh, and running the games directly from the SD card requires the system to have at least the running game's worth of space left as it always loads the game to Wii's memory before running it from an SD card.
So if you have tons of games filling the Wii's space and have tons of games on the SD card be prepared to leave some extra space available in the Wii Mode internal memory too if you want to run them directly from the SD card.
EDIT2:
Oh man, I still remember the days when the SD cards weren't an option...
And when they became an option, you weren't able to play games directly from them.
But later that became possible too, but only with having some space left on the Wii too.