Advice, help, resources needed

Hi Guys.. I am pretty excited. I found a deal, that I think is pretty
good... but I have 5 days to learn as much as I can (luckily I am a
quick study).

In your opinion, is this a good deal... a two year old well established
75 gal salt water tank, 7+ fish (dog-faced puffer, clown, black and
yellow striped tang, 4 Damsels, 4 choc chipped stars), filters (one
UGF, and on hanging), decor, wooden stand, food, chemicals, and water
levels tests... Gravel for the substrate... For $400

Ok - now that we have that out of the way - If it is a good deal, then
I pick it up on Tuesday. I need as much info as I can get... I am used
to freshwater, I was pretty proficient at it, with a well planted tank
and DIY lighting and CO2 stuff...

So here are my questions..What is the biggest differences in fresh
water and salt in maintenance? What do I NEED to know by Tuesday?

My biggest question is what is the best way to transport this tank and
reintroduce the fish without losing alot of the biological filter and
stressing out the fish.

Also - one more that I can think of right now... There were two fish
that I really wanted - I got the dog faced puffer, the other one is a
black lionfish. Would he fit into this tank at all??

And - can I get coral, and anemones with this tank? The substarte he is
using is gravel - should I add live sand, or is gravel ok (I guess it
is ok, he's been using it for 2 years).

Any advice, websites, or books you can offer is GREAT. I am very exited
to learn and get prepared for my new hobby.