Inflatables are robust and stable boats and can cope with a lot. However, the biggest risk is setting off into waves, and — even worse — coming back into shore. From out at sea, you can only see the green backs of the waves, then as you get close to the shore they can pile up as the water gets shallower, and suddenly you're coming through surf. If a breaking wave catches you from behind, it can turn the boat sideways and then over.
Once you're out beyond the surf, in any sensible conditions, you'll be fine. It's like an aeroplane: flying is easy, but landing is where the pilots earn their money. Sibbing is perfectly safe until something goes wrong!
Boating is not strongly regulated in the UK. However, many local authorities and private companies charge a launch fee to use a slipway. Some local authorities also ask you to register your boat before launching it on their territory. This is so they can exercise their duty of care to other water users by checking that you have third party liability insurance. It also gives them a stick to beat you with if you behave badly, such as racing around in the shallows near a bathing beach.
Insurance is easy to get and, depending on the boat, somewhere between about £75 and about £125 for a smallish boat with a small to medium engine. A simle Google search for "dinghy insurance" will help. Personally, I've had excellent service from https://www.alan-thomas.co.uk/privat...aft-insurance/
(I have no connection with them other than being a customer) but there are other well-known names who are no doubt equally good.
Safety kit: buoyancy aids for everyone on board, an anchor with a chain and plenty of rope, and the knowledge of how to anchor properly. After that, the amount of kit you need depends on how much risk you take on. Pottering about on a calm sea with a gently onshore breeze and plenty of safe landing places, you can survive with just a boat, personal buoyancy, windproof top and warm hat, sun cream, foot pump or hand pump, reliable engine, enough fuel, oars/paddles, anchor, chain and rope.
If you are going further, or in more challenging conditions, or where landing opportunities are limited, then you need to kit up accordingly. Your kit requirements will increase as your experience increases.
I suspect that most SIB owners do not do the adventurous stuff you will read about on here. My current SIB manages a couple of easy river trips a year. If I were back to my old days of using my SIB on diving trips off the west of Scotland, I'd have a radio, flares, possibly a reserve engine.