Welcome Vincent & Sally.....
What time of year are you wanting to travel and exactly how far do you want to go in those 5 days???
Western Australia is a massive size....where are your must sees so then we can help you a little more.
Always make sure you have sufficient water supplies, bug repellant (depending on what time of year you plan on travelling), proper clothes for the climate as some places can still get quite cool in summer at night & of course food supplies.
Not sure what the rental companies include in their prices eg: linen, cutlery, crockery, cooking tools, etc.
Looking forward to hearing where you plan to go so we can chat more about what you need to know.