There are some tools that help you run the llm on your device without internet. I'm using LMStudio, it has the user friendly interface.
Then you need a model. There are many Text Generation models, you should have a look at UGI leaderboard on Huggingface, created by DontPlanToEnd. Choose the model with big parameter, big quantization (at least Q6), as much as possible. Try various models to find out which you like most. Previously I used Daybreak-kunoichi 8B Q8. Now I'm trying other models with higher writing points.
You could change the llm config and system prompt, take a look at reddit. Try various prompt type to get the output you like most. Even everytime you regen, it could give you other output.
In my exp with llm, they are good at generate a few chapter. In a long novel, there are some repeat, loop or wrong context after a long time. But it's worth trying.