Can I use blinds and kitchen curtain on my kitchen windows?

Yup. Done that....keeps the drafts down

Of course. I think it looks great !!!

My Decorator told me to only use the blinds + a valance (on a board) and not the curtains with the blinds or it will look too heavy.

Absolutely! I have blinds and then I have just shear curtains that are only on the sides. So I have a large windows that are recessed and have window seats. I put 24 inch rods on the ends and then I hang shear curtains on either side of the window. They don't close, they are just for décor.

Of course you can.

Of course! Just make sure the curtain doesn't touch your countertop. Otherwise it might get yucky.

Yes, I do. For me the blinds help keep the heat out in summer and the curtains to look pretty. I have vertical blinds, then a double rod with sheers and curtains.