You need to show that you comply with the law somehow and complying with approved documents is how you do it. You can't just pick and choose the bits you like. If you choose not to comply with it you need to demonstrate you have complied with the law in some other way.
Any professional doing...
I think you might have difficulty trying to convince a Building Control Officer or a Magistrate that the wiring to the central heating is not fixed even if you supplied it with a plug and socket arrangement.
In any case it is not what a decent sparky would do.
The distance from the corner of a room comes from BS8300 which requires a minimum distance of 350mm from the corner to outlets, switches or controls. Hower Approved Document M doesn't seem to mention this.
I worked for someone that always told us to do 4mm radials for SOs instead of rings. I always suspected he was caught out by the NICEIC not being able to test rings.
What's a bogie?
What you need to remember if your working for yourself, is that you are not getting paid for bank holidays or other holidays and you have to provide your own PPE.
You can be on the link and not be a qualified electrician. A qualified electrician would have done an apprenticeship and have city and guilds or BTEC or NVQ qualifications.
I think there is a good case for not using ring final circuits. I've come accross plenty that have been broken and I suspect have been so since installation. But if they are correctly installed and maintained then they are sometimes the most efficient solution.
I think they are ****e. They have prongs that stick out that the MCBs are fitted to. I don't know if you can get covers for them but I have never seen them fitted and it makes working in the DB live dangerous.
I can't find any requirement in the regs for isolation to be local. Also there is no requirement for a RCD. However I would fit both. I wouldn't fit a shower or replace one without fitting a RCD.
There is no skills shortage. It's propaganda by the government so they have an excuse for unlimited immigration. If there was a skills shortage Electricians would be earning lots of money.