Any ideas on accommodation on the lake?

There is a great lodge and campsite in Cape MacLear (southern tip of Lake Malawi) called Fat Monkey. They are at the beach in the heart of the traditional fishing village Chembe.

It's more of a backpacker lodge but they offer single and double rooms, a dormitory and a good campsite. They also have a bar and restaurant. Get more information on their website http://www.fatmonkeys.com  

Enya

Manda Nkwichi Lodge lies on the Mozambique shoreline at one of the most beautiful points on Lake Malawi. It has been carefully designed to provide comfort and privacy for guests. With a maximum of only 14 people staying at Manda Nkwichi, the lodge can offer guests the highest levels of service in a relaxed and peaceful atmosphere.