Wow so much good advice, I now know I've joined the right forum.
The gas fire is going that's for sure, I already have a 2Kw electric fire I use for camping, I was just unsure of the costs of running it.
A humidifier is also on my list as is a fire extinguisher, there's so much to buy.
I did think about insulating the roof when I was building it but for some reason I didn't. It's a good idea and will most likely be my next major project. I can see the benefits of it that is for sure.
The reason I put a 30mm MDF floor down is that I got 6 1220×2440 sheets for next to nothing. The shed already had a 25mm floor sitting on 50mm square joists so I laid the 30mm floor on top of it making it 55mm thick, I thought it would take the weight of everything. It feels good and there is no movement or bounce anywhere.
As for what I'm going to make in it I'm not 100% sure. I haven't touched a lathe or milling machine for 32 years so firstly just practice making swarf. My other hobby is astronomy and I have a nice telescope set up so will make a few adapters and then design and build my own Alt/Az mount and maybe if I'm any good a EQ mount.
Finally I would love to build some steam engines one day.