Buy The Underwater Photographer by Martin Edge, 4th ed. Then read it. As you practice/learn more, read more or read again.
Get in 20-30 dives with no photo gear before considering taking it. Then start using it on dives with easy dive conditions and reasonable visibility.
Consider practicing diving with photo taking in a pool. You can learn quite a bit about your system this way and it usually costs little. You can learn about your lights and how much light they offer you in perfect conditions in the pool.
I like fiber optic triggered strobes and those work with your housing.
People in the UK can likely provide better insight for lighting local diving.
Hope this gives you ideas for getting started.
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