You're really going for it, aren't you. Camera, a brace of lenses, now accessories!!!
The thing with photography is that you can never have too much gear (try telling my wife that!) and the next piece of kit you 'need' is normally dictated by the last picture you took.
My advice, before any gadetry, would be a decent tripod. If you spend a few quid on a good one it will last you many years. How much you spend will depend on you and what you want to do with it. The important thing with tripods is stability and you get the best of that when the centre column is not extended. So, if you need a tripod to be at eye level make sure you get one that will extend to that with the legs alone. However, if you want to take pics of flowers, or creepy-crawlies at ground level you won't want one that is waist level fully retracted! The next consideration is the head and here it becomes a bit of personal preference; Pan-Tilt or Ball heads? I suggest you go to a friendly camera shop with a good stock of tripods and try them out, see what you're most comfortable with. Any shop will let you play with them in-store.
One final tip. I don't know if anyone still makes them, but if you come across a twist-lock leg - Walk away
