pretty vague information, you need basics like a bed, sofa, table & chairs and maybe a dresser, desk, coffe table, end tables, nightstands, etc. Then bedding, towels, dishes & utensils, etc etc

if you are buying everything new, you could start at a minimum of $1000 and up. Designers/decoraters usually help with the finishing touches like artwork, accessories, color schemes, etc.

That depends upon what you already have and want to use, your budget and what style you like.

It can be as expensive as you like.