please bear with me, lots of questions.
Someone saw my interest in aquariums growing, and they had stuff they were never going to use, so they gave it to me

I am still learning. Currently have a 29g with eclipse 3 hood.
So I got an older 55g gallon tank. Looks ok, and I like the size of it.

I want to have a few fish, rock and some corals.... light limited.
My question is about this wet/dry filter I have gotten, because it looks like mouse trap with all sorts of hoses coming out of it. I will be honest, I have no idea how this thing works, since it came in pieces and the person I got it from had no idea. Anyhow, it is
Amiracle Slim line 50B with an overflow thingy, and a pump. I have been reading about them, but I have so much new info I can't keep things straight.
So if I can conjecture on how I think this works... The water gets siphoned from the tank with the overflow to this wet/dry filter... however it works, it does its thing, it then returns the water to the tank. Would that be correct?
From there I have read this design can flood if the power goes out? I live in a place that looses power a lot.
How loud are these things? I have a small living quarters, so if it is really loud it may be too much for me to handle.
Are these any good? I heard bio balls are nitrate factories from some, and not others? Use a deeper sand bed?
This stuff has not been used for years, should I replace all the hosing etc...? cleaning tips?
Got some power heads

just need to figure out the make and get some parts.
Now to figure out the lighting... good god
Thanks,
Ser