The rules change frequently but if you’ve already had a charger for free you can’t get another (unless you buy another car and have 2 EVs at the property)
As for charging it for 18 hours, we’ll thats very unlikely. Firstly you would need to run it to almost 0% and then want to fill it to 100% so unless you do 300 miles every single day I doubt that’d be a issue. And if you did get home with 0% then you can unplug at any time and percentage if needing to go out, similarly you can just plug it in when you arrive home and most occasions it’ll be full the next day… whats your average daily mileage?
Doesn’t the Kona still have the 80% charge option ?
Personally I wouldn’t pay out for a 7kW charger in your position until I’ve tried living with the car and the 3.6 for a while…..
However saying all that, is your charger cable tethered or untethered because in 2012 the only EVs really available were the Nissan Leaf and it used a type 1 plug where as they all use type 2 plugs now ? so check the plug as it may not be suitable for your new car and if so approach Motability and explain the situation, hopefully they’ll help towards the cost of changing