CB takes 50%, which is quite a cut on a custom, but it does offer you protection. You could consider using ManyVids as a place to offer customs. Payout is 80% on customs and they do cover chargebacks.
As Amber said, you're not really supposed to do customs on OF so this is a risk you would be taking, on top of the risk of being hit with a chargeback. Additionally, if he wants you to say his name, this is something that you cannot resell so you could be making this vid for zero compensation and get into trouble with OF. I personally would not use OF for a custom unless it's under $100 and the person has already 1) purchased PTV's from you and 2) likes the PTV's that they've purchased.
With regards to your prices, it's completely up to you. If you don't feel super comfortable with certain things, but are okay with doing them, reflect it in your price. My prices are quite high. I'm not a huge fan of customs, especially for people I don't know well, and my prices reflect that. I start at $10 a minute. This is for a basic striptease (with no actual nudity shown) and/or clothed masturbation. Any other things that someone wants will have an extra cost.
@MissCJ As far as I know, OF used to be okay with customs. Many things have changed on the site over the past several months, including that. I used to do customs on there every week or so for specific people, but I've stopped doing them completely since I've been back from my hiatus. Occasionally, I'll do a short 5 minute "custom" where I just do something that I know the person likes, throw it into a PTV for $50 - $100 and tell them that I made them something special that they might enjoy. However, I do not recommend doing this unless you know the person and their likes/dislikes really really well.