Questions about Tangs?

[Stege_saurus]

So sometime in the future, I would love to get a Tang or two. I have a 120g reef aquarium and have always loved the look of tangs. My questions are this:
Which Tangs are best kept in the home aquarium?
Is 2 a suitable number for my size of tank?
My LFS recently told me a tip they have when it comes to Tangs: keeping 2 "diamond bodied tangs (i.e. Yellow Tang)" is more difficult than keeping 1 "diamond bodied" Tang and one "oval bodied" (i.e. Blue Tang) Tang. Is this true? Does anyone have any testimony regarding this?
I also quarantine everything I get for a minimum 2 weeks, depending on where it comes from, would 2 juvenile Tangs be okay in a 10g QT, or should I use my empty 55g for their quarantine?

Thank you to anyone who is willing and able to help!

 

[sfin52]

def use the 55 gallon.

 

[Stege_saurus]

The only issue with using the 55 that arises is, I don't have room inside for it. It's sitting in my garage, which gets about 10°+/- as compared to indoors. I would have to find some way to insulate it against the change in temperature...(summer months it gets warmer, winter months it gets colder)