As far as I know, a provisional licence lasts for ever, till you pass
You must inform DVLA if you have diabetes. Depending on the type they will send you an assessment form, which may result in further enquiries and instructions. If you inject that will almost certainly mean you have to test before driving, and then at 2 hourly intervals
You should also inform your insurance company. There are not usually any problems about this, but nevertheless you must inform them.
This means you should have your meter etc in the car with you when you drive on a long journey. For a shorter trip to the shops or something like that I test and leave the meter at home.
But in any case, make a written record of it, just in case there is an incident
Feed the car - by that I mean keep some sugary snacks in the glove compartment. I use jelly babies, liquorice allsorts, and a couple of biscuit bars or cereal bars.
Also something to drink. You can use a small bottle of water or fizzy drink; as you are keeping it to treat a potential hypo it doesn't have to be diet, in fact it would be better if it did contain sugar. But I use those plastic pouches of drinks, like Capri Sun as they fit in the glove compartment easier
You could add a packet of glucose tablets, or perhaps you carry a packet with you anyway
It's very useful to have a headtorch in the car (even if you're not a diabetic) for fiddling about with meters, injecting etc, at night. It doesn't need to be an expensive one, you can find them for a couple of quid in discount stores