Welcome to the forum.
Fortunately owning a boat is still on the whole licence free in the Uk, but that said who knows what lies ahead.
In terms of licences, you can buy a launching pass. Most slipways, there's some sort of launch and retrieve cost. If you're limited to certain locations it makes sense to buy a pass and it will be cost effective in the long run. In Scotland I buy a launching pass which is £70 for the year, April to October and I can launch from a number of Harbours around the North East coast.
If you're using VHF radio, then yes you need a licence. You can enroll at nautical college, and some larger marina businesses run them. There's an exam at the end which I think can be done online. Used to be around £100 but no doubt that's gone up.
Competency around boats, then RYA course include power boating courses. Useful if you're a complete novice and will set you up with an experienced tutor on the water in groups. You can do level 1, but most people go straight to level 2, as obtaining level 1 is not a prerequisite.
Taking you boat abroad, or even renting a boat abroad for craft with engines above 10hp (from memory), then you'll need a ICC licence. International Competency Certificate.
More details here. https://www.powerboat-training-uk.co...ype/powerboat/