Yardage depends on your facilities and what the rates are in your neighborhood.

Around "here", typical yardage is 28-32 cents for open yards with concrete aprons and 35-40 cents for confinements.

Mark-up is usually 10-15 cents on corn, corn silage is 10X the marked up corn price (at 35% DM) 10% on wet co-products and ground hay, 5% on dry co-products and balancers, $2/head for chute charge.

In a way, it doesn't matter how the yardage gets divided up - either you can do it for that or you can't and only you and book keeper can answer that. Regardless of your expenses you can't charge more than the competition, especially when you don't have already have a customer base and a reputation. Which brings up the other challenge - don't bother unless you know you have guys that will place cattle with you. Without any closeouts or cost of gain history to show people you can't do a "build it and they will come" thing.

Most guys that are custom feeders started by feeding their own cattle first and then expanded the feedlot to custom feed (more cattle reduces fixed costs per head). Another way to gain customers is to be willing to partner with them on pens of cattle.

Good luck.