Your cage size recommendations are too small.

My yellow is a female, 3 yrs. old, around 10 foot and lives in an 8x4x2. She has a large tub for soaking, good hides and is never in the same place for very long. She's a sweetheart to handle and is absolutely gorgeous.

If you have an RTB, I see no reason why not to get a yellow. They can be nippy at the start but regular handling will get them out of that.

Good luck, and definitely buy a neonate.

As for the monitor/tegu, they are ultra cool and much more work intensive than any snakes.

Chris