youve ticked the certificates box and if you apply they will get you to do there tick the right answer test on your computer at home so you can look up the answers.
For assessment you need the relevant books, a mft with calibration cert and other documents they give you on the website. plus insurance.
as for the job, they will accept for the first assessment, a job in your own or families house, such as a CU change, new circuits etc... it basically needs to be able to let them see you can test and interpret properly.
Its quite an outlay for occasional work, if working for others and charging you need some experience behind you.
You only need to join a scheme if you will do notifiable jobs, as long as you arent daft why not start out do odd little jobs and issue generic certificates, then when ready apply to a scheme.