1.What is a good camera/setup for beginners in underwater photography?

(1)It depends on what you want to do. if you just want to get in the water and shoot without worrying about settings, an Olympus TG.

(2)If you want to get into underwater photography and learn how to use all the settings, it’s recommended to you a compact camera that has a manual mode (such as Canon G7Xmkiii). 

(3)Once you feel you can't squeeze any more out of that camera creatively, then you could progress to a mirrorless or DSLR

2.How is the vis for night diving? How to change your setup for diving at night?

(1)Actually, vis is not really important during a night dive as you can really only see so far in the dark. As long as the conditions are 1 - 2m visibility, you can still enjoy a great night dive.

(2)I don't change my setup at all, just make sure I have a focus light as a torch and to help my camera focus on my subjects. Also, always good to have a backup torch (Orcatorch has lots of great torches for night dives).

(3)For the cave’s I use 2 lights, and I use minimum 2 flashes, then on my model or behind a corner I use flashes with a trigger. In cave’s you need a lot of light.

3.Do I need to make changes to my photography setup depending on the subject I’ll be shooting during a particular dive?

You have to decide in advance what you are shooting - macro or wide angle and set up for that. For me, I add a snoot and a diopter to my standard 2 strobe setup with macro, just in case I see something that would look good snorted, or if I see something that is super tiny that needs some magnification :0 But yes, I try to be ready for anything. Luck would have it that the macro dive is the one you see a rare shark or a dolphin on your dive though.

4.Which dive torch or video light would you suggest as a first focus light for a compact camera setup? 

I would recommend the D530V with or without the snoot adaptor if you are looking for something small and compact. If you want something larger, that will grow as you progress, definitely, the Orcatorch D900V is also a good choice for UW photographers. Al depends in what kind of virement you are going to take pictures. 

5.Any tips for reducing backscatter and increasing video quality in lower viz conditions?

Re backscatter for video, you could try to make video without using your underwater video lights (all of Indigo Scuba's videos are made without strobes). That way the torches don't reflect any backscatter. The other option is to pull your torches behind the front of your camera / GoPro so that the beam does not light the water between your camera and your subject. It's pretty difficult, so we tend to turn ours off. BTW, if you are using a GoPro, visibility always seems to look better than it really is. 

6.How do I position the snoot? Right on top, or in front of the subject?

You can position it on top for a circular pool of light, and diagonally from the front if you want more of an oval light.