I think it depends on the scale of the thing. If it's just a small cafe in some town, nobody's gonna care. If it turns into a huge chain and you expand everywhere and make huge profits, then yeah their lawyers will probably start contacting you.
It very much depends on the company though. Nintendo (and TPCi) are pretty lax about this, whereas others like Disney and Sanrio are ruthless at defending their IPs.
source: have made and have friends who make fan merchandise, where it's the same rough idea.