Hi etwee:
I'm a newby oscar fishkeeper too, but I can tell you that 40gal is not suitable to keep just one single Tiguer Oscar (or any Oscar). It is true that at 6cm they look like cute babies -which they are, but they grow so fast! I suggest that you start by reading, all the useful info in this site.
I live in Santo Domingo, Dominican Republic, but I guess any Local Fish Store would have test kits, please look for liquid reagent test kits, strips are, for the most part, unreliable and not accurate.
There is a section on suggested compatible tankmates for Oscar fish. But the size of your tank is of paramount importance, as well as your filtering capacity.
If you are patient, and take fishkeeping seriously, you could easily learn, as I am learning, to care for Oscar fish the way they deserve. This is an incredible fish that requires good care -maybe not as much as Discus but they are delicate tough fish!
I can't tell you how personally attached I am (in fact the whole family is) to our young Tiguer Oscars. And they've been around for a short time (one a month or so, the other one came home last Saturday).
Don't let the info overwhelm you, take your time. And enjoy the ride. Did you know an Oscar could live for 15 years? Think about that for a while...
Pepe
Santo Domingo