On the lighting side, it depends on how the existing circuit is wired.
I'll guess based on a single light at the moment.
There is 1 of two ways it will be wired.
1) A cable from the CU goes to the light then another cable goes from the light to the switch.
In this case you would run a cable from light 1 to where you want light 2 and then run another cable from where you want light 2 to where you want the light switch to be.
2) A cable comes from the CU to the light switch then another cable goes from the light switch to the light.
In this case you would want to run a cable from the light switch to where you want the new light switch, then run another cable from the new light switch to where you want the new light.
On the sockets side. I don't know. I have a feeling you may need to upgrade the 20a circuit to a 32a ring main but there are others on here who can better advise. Bear in mind if you have to upgrade it might mean having to upgrade right back to the main feed from the house CU depending on the cabling used at time of install.
Hi no way will you be able to load existing supply as you desire,
drier 3 kW small heater say 2 kW = 21A without any other load.
Futher you should get the PartP leckie who is going to do the connecting to either run the wiring or at least agree to routes first as he will be certifying as if he has done the whole job & is unreasonable to expect him to do so without some input early on.
He should also be able to indicate what sw/lt wiring will be needed,
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!