So, after seeing Lizaan's new shoot ( and almost dropping my phone in the proses mind you), I was wondering : is it appropriate for a client to ask a lady to dress in a certain manner for a date? How practical is it really for the girls to say, dress up like they did in their shoot?

Dressing a certain way or in a certain outfit can be problematic for ladies working from a venue and not in their own space. So my advice would be:
Set an appointment the day before with your request. That way she knows to pack the clothing that you would like to see her in. And please do honor your appointment because if you don't you will ruin it for the next guy that has a similar request because she will remember that you made her pack all that and take it with and didn't show.