Hi @alexbelotsky, welcome to the forum!
To increase the length of your response you can try to integrate something like “reply with X paragraphs of text” or “Reply with X words” or “give me a detailed response”. The model tries to answer your requests as concise as possible because that is what most people want. So if you tell the model you want a longer answer you’ll receive it in most cases.
Secondly GPT4 is not what you buy when you buy the ChatGPT Plus thing. GPT4 is more like a add-on. In my experience for most usecases GPT3 performs sufficiently 