I would suggest you do a full eicr in great detail before anything else.
Then you will know exactly the state of the installation.
For most of this you wouldn't need a mft, as you would gain great understanding from just looking under the covers, this may be enough to decide in any case, then get a tester for the testing aspect - at your own home you can spread the work out and do 100%
Then decide.
Although, I would think about putting a bigger rcbo cu in place and check out the earthing in any case - is it TT?
You would likely need to add/upgrade smoke alarms etc in line with the new law
There should be no reason to automatically need to replace the red/black pvc stuff, but you would probably want to extend or change stuff to match your future needs