We only say " loja de roupa " or "boutique" if we're writinh a foemal text. If we're having a simple conversation se just say "loja", like you said

Loja de roupas. Only shop is "loja" in portuguese.

Clothes shop say in português - Loja de roupa Loja = shop Roupa =Ropa

Depends, can be Loja (is general, Clothes, Eletronics, etc...) de roupas or Boutique (generally be located in Shopping Centers).