I'd say the most important accessory to get is a Razan washable hose, or just any washable hose for that matter (But, ya know, Razans are the best, right?!
). Unwashable hoses can realllly become a royal pain in the ass after a few months sometimes, and like you said can leave a bad taste.
Also phunnel bowls are great for longer sessions (2+ hours depending on which size you get, and how many sets of coals you decide using on it) if you plan on smoking long sessions or with friends, or smoking really really wet shisha (because the phunnel doesn't allow the juices to go down the stem as egyptian bowls do). Ultimately though, as Sambooka said, the most important accessories to your hookah is finding a good shisha and coal you enjoy. :P