I was thinking about getting this but if there is a very small limit on how much I could create then I won't bother. So is there a small limit or...like EarthBound size coding room?
As with any other platform, resources are limited. However, you'll find out that these resources are still plenty for creating games and software.
Here are some of SmileBASIC's technical specifications:
Full 3DS screen resolution.
6 graphic memory pages.
24 simultaneous sound channels.
Up to 4 dimensional arrays.
About 8MB RAM.
Processing power similar to SNES (approx.).
You may think it's not much, but you can program a huge variety of games with it. It's definitely enough to make an EarthBound-like game. There are more tech specs you can find in SmileBASIC's official website.