Ok as a 7 year old diabetic im going to give you some very simple pieces of advice.
Do not keep your emotions bottled up for the next few weeks, your better off getting the rant and tears over a done with as quickly as possible (Even better if you have an other half you can just curl up in a ball with

).
Next up is the diet change, you'll be asked to do the dafne course which is basically an idiots guide on how to control yourself. Rule of thumb is your not allowed these 4 things: Sugar, full sugared pop, boiled sweets, and finally fruit juice
Everything else diet wise you can keep as long as you dont have high amounts of sweet things, slice of cake etc with a coffee is fine if your having your fast acting insulin along side it.
You will have hypos and hypers again at some point, remember to have some form of quick acting sugar with you at all times and your fast acting insulin handy.
Inform the DVLA and any insurance companies you have too!
The hardest thing ive found is the testing, i do test every now and then, not as much as a should, but i can tell what my BG is sitting at from experiance
edit: I was diagnosed in Geneva whilst on a 6th form trip to CERN, those were fun times