Welcome!
What you propose sounds like a reasonable approach if you have a qualified mate who can do the design/specification side and essentially supervise your work as it progresses and do any critical bits they feel are beyond you. Depending on what course(s) you do and any tools you buy it may not save you much money, but if you want the satisfaction of knowing it is done right or have a longer term goal to work as an electrician then it justifies it.
What most folk on here would be concerned with is your safety. So you should be learning about safe isolation first, the practice of making sure what you are working on is definitely dead, and stays dead! There are some useful guides here:
Electrical Safety First produces, in association with other industry bodies, a range of Best Practice Guides which provide definitive information and guidance on a range of technical subjects.
www.electricalsafetyfirst.org.uk
In particular #2 (safe isolation), #4 (inspection codes), and #1 (replacing a CU). Also they provide this guide of CU replacement with a few illustrations of common mistakes:
For many of the jobs you won't need any special tools beyond making sure the circuit really is dead, typically just a set of good screwdrivers (ideally the VDE insulated sort just in case), cutters/stripper type pliers, and a handful of the typical DIY tools for fitting the accessories in place and routing and fixing the cables.
For the more critical jobs like CU or high current connections like a shower, etc, a torque screwdriver is now recommended. Many experienced sparks don't feel they are worth the money as they know from years of experience what is "reasonable" for a given type of terminal, but as you don't have that experience (or for those working in an industry with strong regulation on such matters) then such a tool avoids the risk of too tight or too loose a connection.
But don't forget PPE like a dust mask, goggles (drilling or chiselling, etc), ear defenders (if using a noisy power tool) and a hard hat if going in to an old style attic with nails sticking down from the slates being pinned in place!
Your mate should be able to advise if you don't already have a collection.
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If your mate is going to do the testing and signing off then you won't need to do that, but if you are also planning on replacing easier sections on your own you should have some test equipment. Short of spending £500-1k on a Multi Function Tester, you should be looking at the following sort of tools:
- Voltage Tester (simple "is this live?" check)
- Proving unit (to test the tester)
- Socket tester (even £10 model verifies L & N polarity, £50 one also checks Earth resistance)
- Multimeter (at least CAT-III 300V rated)
While you can do all of the tests with a multimeter, it is also easy to get it wrong and when your life depends on something being dead, you don't want to accidentally measure using DC volts instead of AC volts and you end up the one being dead!
Also if looking at meters, you should get one that is safe to use on
high energy circuits so if you do accidentally connect it to 240V mains on the wrong range it does not explode in flames in your face. That is why the CAT-III / CAT-IV rating matters!
Just look on these forums as often there are threads discussing choices of tools and test equipment.