Can 'normally' be used instead of 'usually'?
They're the same: I don't know whether "normally" is in the system as an accepted option, but if not, I'd say report it.
I definitely consider normally a valid option, but it's not recognized.
what is the significant of using "ev tasarlarım" and not "evler tasarım", since it is design houses (house plural) but not house designs (design plural) ?
The infinitive is "tasarlamak" and it means to design.
Would "...…..,araba değilim" be correct here as well?
No, that would mean: I am not a car