Before getting on an e-bike a good quality cycling helmet could save your life if you fall off. For a s-pedelec you must have a moped rated helmet.
In addition, you need good lights. Mirrors are a requirement on s-pedelecs and good practice on an e-bike.
As far as clothing goes, it really is up to you. You can wear your normal clothes or be lycra clad from top to toe.
Helmet cameras are great for documenting your journeys and for evidence if there is an incident.