A question for parents with stepchildren?

I am pregnant with MY first child. My husband however has an 8 year old son that he is planning to try and get custody of. We've talked about this and we feel its best because his mother is having issues with her marriage... Has 2 other children and is pregnant with her 4th. We feel he is not getting enough attention from the way he acts when he visits. His mother rarely brings him for visits even though the court said she had to bring him more. Now here's my issue. Since I haven't been around him too much I am afraid he will not accept me as his stepmom once we get custody of him. He is usually very well behaved and I have never had to discipline him and honestly at that age... I have no idea HOW to discipline him. I would think that's getting a bit too old for timeouts and corner time. Any suggestions from anyone would help... I guess I'm just asking... How do I know what to do with him? Will it come naturally as situations arise?