I have some tips for travelling Xiamen for these gus who want to go there by DIY tour:
1\ Hotel Booking: The best location should be around South Putuo Temple. Becasue these major spots are near around, and you can take buses easily.
2\ Time arrangement: You can spent about 4-5 days to explore Xiamen's major spots, which I means: South Putuo Temple, Gulangyu Island, and Binhai Road, Other spots are very small in my mind. If you have enough time, you can also explore some other spots.
You can explore South Putuo Temple and Xiamen University in the first day;
And then one or two days will spent in Gulangyu Island;
Then you can ride bicycle with your friends on the Binhai Road, and there are many facilities you can play along that way.
3\Dont forget to enjoy the wonderful food when you explore the city.
Here is a street named Taiwan Delicious Food Street near Gulangyu. You can eat many kinds of foods in that street after explore Gulangyu Island.