Replicating your AdWords campaigns on YSM isn't as simple as you may expect.
The main reason for this is that Yahoo will only take an advert if its exact match has a search history. This means that if you want to advertise for many service/locality combinations a large proportion will come back as rejected, even though Google has shown there to be traffic for those terms (on broad match).
The best way to tackle this is to ask your rep for a proposal, if you have a patient rep you can send them thousands of combinations and they will come back with a spreadsheet that has the acceptable ones along with a few options for costs (this makes it simple to work with).
You don't have to go with their cost suggestions, but you will have to be willing to spend several thousand pounds (UK) a month for them to do the proposal. That's not usually an issue if you cover a large enough area.
The other big issue is making sure you get your bids and creatives right from day one, you don't want o be fiddling about often in a user interface that is as frustrating as YSM.