Please don't be nervous. A homecheck is part of the process for the rescue to make sure you are matched with the best possible dog for your family, and to do that a home visit provides lots of info. The homechecker will be looking at the safety/security of your garden/house (important for a lively dog that can jump or tunnel), and will want to have a chat to you about your expectations/family set up/routine.
It's also a very good opportunity for you to have a chat with the homechecker about some of the little practicalities. For instance you might be undecided where to put dog's bed, or want advice on good local vets, training classes etc. Your homechecker will be experienced with the breed and usually fairly local so they can be a treasure trove of info and support. They are NOT there to inspect your house, couldn't give two hoots about your dusting and also must respect your confidence/privacy.
Usually, the final decision on whether the adoption goes ahead is not made by the homechecker. After the visit, they will report back to the rescue and discuss what they've found. The rescue will then decide if the likely pairing will work, if another dog might be more suitable or (rarely) if the family is not suitable for adoption at all.
Bringing along the homechecker's own dog is often to see how you will interact. If you start hyperventilating at the thought of dog hairs on your rug (and yes, this does happen!) then it probably means dog ownership isn't for you. If the homechecker practically has to shoehorn the dog back from you after extensive snuggles, playing, etc then they will be very much happier that you are a doggy household with a genuine love for the breed.
Good luck!