Whatever size you think you want, go 25 to 35 percent bigger or you will be doing another build later. Just speaking from experience. Another thought to consider since you have the perfect room for it is that a peninsula is so much more satisfying because you have three sides to view the tank versus one on a regular tank. You have so many more options for rockscaping with a peninsula also. And go as wide as possible, your fish will thank you for it and honestly theres no need to vacuum the sand bed so don't worry about having to clean it, as long as you don't overstock you never have to disturb the sand bed it will take care of itself and be much more like what you would find in a natural coral reef. Regular water changes will keep your reef healthy with no need to disturb the sand bed. Just my 2 cents worth, have fun!