Cages first then snakes.
There is a difference between a neccessary choice (ie... cage breaks, malfunctions, and emergency dictates that you need to place the snake safely in with another only temporary) and the purposely wrong choice of exceeding your housing limits intentionally. If you know your out of cages, get some more before buying the snakes.
If anything silicon in a piece of laminate or plywood and seperate each of your giant aquariums into two smaller cages.
For your question of pairing. As a general rule, never put two male retics together, sexually mature or not its a not a good habit to even start.
Lastly its always wise to have a spare cage or two around for such instances of emergency housing, cage replacement/repair, or impulse buys. just be sure to replace it if you make a permanent collection choice.
-Notah
>>I was just wondering, if you had to make the choice between sticking 4 retics (2 males/2 females) in 2 cages, which would be better for juvi retics about 4-5 feet long: two males in one cage and two females in another or a male and a female in each cage? Am thinking of getting some more snakes, but I am quickly running out of descent cages. One cage is a 125 gallon, the other is a 75, by the way. Thanks a lot!