Great boat for the broads - congratulations on your purchase
I carry mine (2x Adventure) on the roof of my XC-70 no problemo.
I carry them in kayak cradles which allows them to travel right ways up - I find this much better than upside down as
1. it is easier to load them singlehanded (I have already posted on the technique so have a dig around on the forum) and
2. you can then use them as a top-box by filling them up with all the gear that would otherwise fill the car up - the paddles, masts, sails, fishing rods, clothing, PFDs & cart all go inside and I even carry heavier items in the load tray under the bungee.
I always transport them backwards... (no, I don't reverse all the way to my destination
I load them onto the car so that the stern of the boat is pointing in the direction of forward travel) this means that you can leave the seats in place (just unhook the seatback bungee & fold the back down) and the rudder doesn't really need to be bungeed as airflow tends to make them lie flat rather than lift up.
As to clothing - it doesn't get half as cold here in NZ as it used to in the UK where I used to do a lot of windsurfing year round. The problem was always the extremities - when windsurfing you need to hang on with your hands and you simply couldn't get gloves which would keep your hands warm, not cut off the circulation to the fingers and allow you to grip in the winter - mitts were useless but might work for kayaking. Your feet weren't too bad because the boots we used to wear tended to fill up with warm water sluicing down to the feet from inside the wetsuit - this won't happen when you are sitting down with your feet raised in a Hobie kayak. Here in NZ I have a pair of waterproof kayaking pants which I use with a dinghy sailing smock in the colder weather in our winter (which can give similar conditions to many UK summer days); I suspect that pants with feet in them would be required in the UK. The key, I believe, will be either to stay dry or, if that's not possible, to keep the wind off wet skin. One good thing is that since you really don't need to paddle much, if at all, you should be able to keep your hands pretty dry and therefore warm, and you won't be subject to the constant dripping of water from the paddle which to me was always the bane of using a paddle in cold water. My mate was a builder & he used to swear by 2 pairs of washing up gloves in the winter - one pair worn over the other - dunno if this works cos I never actually tried it, but it wouldn't be too costly to experiment before shelling out on fancy schmancy kayaking gloves.
Hope this helps.