Welcome to the little family, Donna. Martha/ MLyle built a Garfield and had gone back to wire hers using round wire, which can easily be placed behind baseboards and run up either the corners or front edges of walls just behind finishing trim.
You will find building a monster big dollhouse like the Garfield less frightening if you invest in a few rolls of masking tape or blue painters' tape and dry fit things before committing to glue. Not only will dry fitting help you by letting you fine-tune the fit of tabs and slots as you go, but you will be able to see the areas (such as stairwells) that will need to be decorated before walls go up or stairs go in, making it impossible to get your hands in there later. Also, to see what you will want either to prime or stain first. I find that the house often begins to speak to me and tell me its story and what it wants during the dry fit (if not before). Finally, you can sometimes find how to noodle a facet of the construction that wasn't clear from just reading the instructions.