Diving on Mallorca, Spain

I just finished my PADI Open Water Diver certification today. I’m going to Mallorca for a week next week, and I would love to get some quality underwater time while I’m there. I am soliciting the SMDB for some advice:

Diving centre. I have found numerous PADI centres online, but I’d like to hear about personal experiences and (counter-)recommendations. Security, professionalism, friendliness, price are all factors. While I presume all centres have English-speaking staff, I would be most comfortable around native-English speakers; you can’t be safe without feeling safe, and an awkward language barrier will undermine that feeling as well introduce potential communication errors.

Dive sites. Being a novice diver, I prefer to start with straightforward sites with maximum visibility and geographical simplicity. I like flat, I like sand, I like interesting, colourful, harmless fauna and flora. What’s to recommend?

Marine life. I know Mallorca offers a great deal of marine life. I’m not too keen to expose myself to box jellyfish or end up as shark bait. What should I expect to find? Anything non-obvious I should stay away from?

Snorkling sites. Does Mallorca offer any particularly good shallow lagoons, inlets or similar places where one can snorkle in peace without being swept to sea and/or the bottom by malevolent currents?

Diving equipment. I intend to buy a semi-dry combo (5mm neoprene inner shortie + 6.5mm neoprene outer suit) to dive in my own country, where the water is a comfy 20C in the middle of summer, and often lower. How compatible is this kind of suit with a climate like Mallorca’s?

I am asking for facts, not fishing stories. However, a useful anecdote (“a barracuda took my arm off because it liked my shiny wristwatch, so don’t wear one”) is always appreciated.

Thank you!