Other essentials will include:-
Obtaining the correct formal qualifications..
Undertake some supervised practical training, including real world hands-on experience..
Buy all of the BS7671 & other legal documentation relevant to the area of work you are interested in..
Have a decent set of tools including approved calibrated test meters..
Buy some public liability insurance..
If you want to self certify any Part-P notifiable work then google the various membership requirements..
Invest some time and effort into advertising, marketing & promoting your new venture..
Either learn how to do your own accounts or find and accountant..
Be prepared for several years of hard graft as most business start-ups fail within the first 5 years..