It is rather hot in the end of September, T-shirts with skirts, shorts or slacks are the best choice, and It would be wise to bring sun block with you. You are suggested to book the hotel as least one month earlier during the travelling peak season(National Day in October). You may choose the hotel with your preferred location and price in this website directly. Besides, travelchinaguide can arrange the Private Tour in Guilin as per your request, you can send e-mail to travelchinaguide.com|hotel about your request to get the details.

base on your situation, you'd better rent a hotel for monthly. There are some hotel can service for long time not daily. As I know, some local people have building, that's cheap, just RMB20/night or a little higher. But I'm not sure is that still have rooms.