question on adding new tegu to my current tegu's cage

[Venom6547]

So I have a 8x4x4 enclosure built for my black and white argentine tegu and I wanted to get another tegu so i had a pair to possibly breed but i had a few questions on how I should introduce them if i did in fact get another tegu. I already know what i have to do about feeding them and how to control that but does it matter if the next tegu i got was a argentine red instead of black and white? I am also going to make sure they are not both males, mines possibly a female but I dont know yet, is it a problem if i had 2 females? I don't mean to ask a million questions but the more I know the more I will know what to expect and if i should even get another tegu to house together with my current one. and lastly does size matter too much? I went to a pet store near my house today and i found a red, this pet store isn't well cared for and they just got the red so its healthy as of now and I don't wanna jump the gun but at the same time I wouldn't want to let that animal get sick, in a cage maybe 7 feet away from the red was a baby columbian and it was dead in the water dish.. I'm torn between getting a tegu from there because of the reputation but at the same time i don't want that beautiful red going through what the columbian had too..