When I fitted my first SPU there was no MCB feeding it, by time second one fitted there was, the 100A isolator is not big enough for expansion as the total input to the system has to include my battery and solar panels, OK easy enough to add a 100 amp fuse, but clearly this needs to be taken into consideration, I have all RCBO's which means 4 or more extra slots as no RCD's fitted, and all the 16 ways are filled.
As to EV charging it depends what is in the charger, if no 6 mA detector may need type type B and if using an inverter may need type F although unlikely my inverter instructions states type AC which was rather a surprise.
As said notifiable work, so in Wales that will cost £100 plus vat, and if the council want they can insist it is tested by an inspector of their selection which can easy add £200 to the price. Also they will say when you can re-energise and can insist that the DNO draw and replace fuse, so the total cost can go up to £500 or more above the price of materials. And you may be without power for up to 14 days while the work is being done. I know in theroy one can DIY but in practice it will likely cost more to DIY than to get a scheme member to do the job.
I can see the point in using an MCB to supply a sub board like the garage, or the SPU, but if going to use RCD's the first point is to test leakage before starting. I see you have got up-stairs sockets with down stairs lights, etc. However if there is a problem, the up/down split means until problem solved likely extension leads up/down stairs, one should aim to have at least some sockets on all floors which can be used with independent RCD protection to other on the same floor, be it a socket on the cooker outlet, or an UPS supply to freezer, looking for if there is in the future a problem one can supply essentials without extension leads up/down stairs. And of course if some one does get a shock from a sockets supply one does not want plunging into darkness as well. My house is split side to side for sockets and up/down for lights, which means at least 3 RCD's are required.
I have tested my house for leakage
and have 8 mA for whole house, but I would still not want RCD's if it can be helped, I had a roof leak and was able to isolated the sockets in those rooms until corrected, had I had RCD's could not have done that.
You are talking about design, and one has to sign the installation certificate for the design if doing that, the hurdle is getting the LABC inspector to agree to you doing that, I had a right problem with mothers old house, builder ran off, did not have any contact details for the electrician he had used, could not find a scheme member to take over the job, so forced into DIY, but son and I both had the standard three certificates regs and the two inspection and testing, but the LABC was not going to accept them. My son said I had a degree in electrical engineering and only then did he back down, it is not so much the cost of using the LABC but the delays, while you wait for them to inspect.
