Jacob is right on the mark. Everything in real estate is based on comfort level (not including actual numbers or legal ramifications). Agents that specialize in rental real estate are preferred, if not mandatory. You can't just use any real estate agent. If there is an agent that specializes in $500k+ luxury homes, they may not understand the investor market. Use a realtor that has sold to investors, and ideally, actually has an investor list.
Attorney's can help you sleep at night, but they can also keep you up at night with their fees. I would suggest a property manager that is understanding of current real estate law. Once you have a large portfolio, enlist the assistance of an attorney to set everything up into an LLC. That way, if you're ever sued, they can't go after your personal assets. Attorney's can cost you more than the profit you receive from a property, so you have to be careful.
Our attorney is someone that we could not do without because he handles everything that we are not capable of understanding ourselves. They should be a resource and not a liability (financially speaking).