I spent eight days in Funchal at the end of May on an escorted holiday with Riviera Travel. I've written a detailed blog with lots of pictures which is here. Your post reminds me I haven't done a trip report for Slow Europe!
How much free time will you have? Funchal is a place to explore on foot. There are plenty of companies offering day trips around the island and I saw several kiosks along Avendida do Infante.
Thank you Eleanor. The blog looks amazing and such beautiful photographs. I have only had a brief look but I will look in more details soon. I believe I will only have limited time so walking around the city is likely to be my best bet.
You will enjoy Funchal. The street plan is based on a grid pattern so it is difficult to get lost.... There are some superb gardens, and Jardim de Santa Catarina are a good place to drop out. The architectures is great. The inside of Igreja do Colegio (the Jesuit Church) is absolutely stunning and much better than the Se Cathedral. Even if you are not a great one for churches, this shouldn't be missed! The market is wonderful too. The one place I did regret not getting to was Sao Joao Baptista Fort, but it was a very hot day and a steep climb uphill. The views are supposed to be very good.
If you have half a day consider a trip to Monte (bus or cable car). There is also the tobaggan run, but I'm afraid I chickened out of this. The Palace Gardens are worth visiting, or take another cable car to the Botanic Gardens.