and if they were 10cm???

No. I wouldn't do that trade. Rather buy those as slings. You can buy all of those except Brachypelma Albiceps (Golden Red Rump) here: www.petbugs.co.za or www.mrtarantula.co.za you will be losing a rare snake for extremely common tarantulas. Those who don't like snakes will tell you to do it but they don't know the value of the snake. Where are you at? If you were in Bloemfontein I would swap you way better tarantulas for that snake.

seems to be a better idee start small and work yourself up....that way you get some xp aswell..

I am in Durban!! but am looking for mature T's to breed!!!

At 10cm they will not be mature though. Probably a year or 2 to go if you manage to find males.

What color phase is the ATB? I rate that it's a fair trade for nothing other than Garden Phase ATB. garden phase is a fairly common snake, if u have no sentimental attachments to the snake I reckon it's a fair trade IF the spiders are females. You really don't want to breed any Lasiodora (salmon pink) or B. vagans at the moment.
Try get more info on them, unfortunately sexing them accurately is only possible with a fresh molt. So it is a risk, I say do it non the less! Welcome to the hobby!