I will be doing the job myself before moving in and it will be inspected and tested by a qualified electrician.
A qualified electrician (or more correctly, one registered with an appropriate body for Part P work) cannot certify other people's work. If you do the owrk yourself then you'll need to notify your Local Authority Building Control (LABC)
before starting work, and they will provide you with a completion certificate when it's finished. My LABC charge around £150 for 'minor' electrical works if you can provide test results (which your sparky could provide), and £225 if they have to do the testing (or rather, pay a local spark to test it). I;ve seem comments on here suggesting that some LABCs charge as much as £400 for minor works
For a whole house reqire the fees would be a lot more, I'd suggest checking that out before you make any decisions.
If you have an electrician who is a member of a suitable registration scheme and with whom you get on well, it would be best to discuss the job with him and in particular discuss how you might split the labour. If he is amenable, then he can let you do much of the hard work - but of course he'd need to be confident it'll be done to a standard he'd be prepared to put his name to.
He should, of course, be familiar with the regs, and be able to do all the calculations required.
By the time you take into account the LABC fees and the fact your were going to pay him to do testing anyway, then the extra cost of having him do the job with you doing the manual graft may not be that much extra.
I noticed you mentioned moving the meter will cost a fair amount. Why is this?
Because it does
Only the DNO (Distribution Network Operator) can do it, they are responsible for the supply up to the output terminals on the meter and it is illegal (apart from the safety aspects) for anyone else to fiddle with the supply upstream of that point.
If the existing meter is in an acceptable position, then an alternative would be to run a submain from the meter to your CU. it will need suitable means of isolation and overload protection - typically using a fuse to (amongst other reasons) provide discrimination between that and your downstream circuit protection (almost certainly MCBs these days).
As to some of the other questions ...
AUIU, there are very few circuits which
must be RCD protected, but RCD protection is bar far the easiest way of meeting certain elements of the regs. And the cost of RCDs is now such that it makes very little sense for circuits to not be RCD protected except for specific requirements (such as a dedicated supply for a freezer or computer).
Personally, I'm quite in favour of RCBOs - that way you get individual RCD protection per circuit and it avoids all those "which circuits do I put on which RCD" questions when trying to minimise the impact of faults on other circuits.
As for the possibility of Solar PV, I'd suggest installing a large conduit between loft and CU location so that the cables can be puled in later. These may be quite large, so you need to be quite generous with the conduit size - work on the basis that "what'll take a lot will take a little, but not the other way round" and you really want to be chasing out for this once only.
I'd suggest consulting someone who knows about the subject, I don't know what restrictions there may be if the DC is fed down (inverter near CU rather than in attic) - it'll be non-RCD protected and so may need a certain level of mechanical protection.
And as someone else said, now is an ideal time to ensure that you have all the TV/Satellite/Phone/Data you might need. You can need from 1 to 4 coax cables at the main TV point, and many TVs (or set-top boxes) take a network connection or will do in the not too distant future. Sky boxes may need a phone line. If you wanted to pipe HDMI (eg from a Sky HD+ box at the main TV to a TV in a bedroom) then most extenders require 2xCat5e cables. And so it goes on.
Using decent sized conduit (which goes INTO the box, not stop short and not be lined up with a hole) will give you some degree of flexibility as you'll be able to add/change cabling later without ripping up your decor.