Right now around here (I live here in your market) if you are talking basic turnkey - nothing specialized - you're going to be right around $200/sf finished, not including permits or ancillaries (IE you need a bigger septic system, you have to do major grading work for the addition, etc).

You want someone who's been in the business for years, working full time specializing in what you're seeking to do, because if anything goes wrong with the transaction or the house after closing, it can create friction if you think your friend didn't protect your interests.

Integrity goes a long way.You can also give a very generous closing gift, offer additional information/services post-closing, and/or offer a rebate for a portion of your commission at/near closing time. 

Find a lawyer who specializes in landlord-tenant law in your state, and not only that, but who know the rental and property management business well.

What makes you special? 

@Steele KruzelI recommend finding an accountant that specializes in real estate taxation.

Find an investor-friendly agent in your area — some RE pros specialize in foreclosure, so if after research you're confident that that's the way you want to go, I would find one who can work with you and help guide and represent you in your next transaction. 

Thanks to a special IRS tax loophole, homeowners can exclude $250,000 to $500,000 of capital gains from the sale of a primary residence, so long as they have lived in the property for two out of the prior five years."

Do you have any special objectives or projects you're currently working on now that you've been in the game for some time?

It's really about finding those good contractors who can give you accurate quotes and timelines, as well as having an expert agent / broker who specializes in investment real estate and can help you identify these properties as soon as they hit the market.