Hi...here is my opinion;

1. You should tell the designer your taste. Normally what i've been practice, i ask the owner how they wanted to be, for example, contemporary design, classic design, modern design, industrial design or very budget design. But then there is sometime the client ask us to suit with their home layout.

2. Budget may varies according to items the contractor proposed. Mostly the clients loved the custom furniture, facade, balustrade and etc2. Eye candy materials quite expensive, but there are some items cheap too.

3. Electrical appliances depends on market price. Most likely price is fixed and got little discount only. If bulk quantity, got discount more.