1 Yes because he learns Iron head lv 25
2 Yes but that´s doesn´t mean the offspring would be Female
3 You can catch one yes
4 you could breed one if you wanted
First Rough Skin is Hidden Ability which you can only catch in Friend Safari. So you have to catch a female Gabite with Rough Skin and breed it with Aron and you got yourself a Rough Skin Gible.
So skip step 3, 4 ,5 then and you just earned a a HA Gible.
If you need a Gabite safari and doesn´t have one check the friend safari page