If you have a buyer's agent picked out, they can call the owner of the house and ask if they work with agents and see what they would be willing to pay.
You don't HAVE to have an agent to purchase the home, but it can be to your advantage to have an expert on your side in making sure all details are attended to. You also want to watch out for the contract side of things - agents can use their realtor contracts which have been blessed by multiple attornies, whereas in a FSBO situation the contract might have been bought at OfficeMax or something - which can be a little scary. Some of these can be VERY one-sided.
As far as asking the seller to pay your closing costs, this varies from region to region. What is standard practice in one part of the country doesn't apply to others.
When we sold our house, our buyer wanted us to pay closing. But that's not standard practice in our area so we NIXED it - the contract they had presented to us was from a friend of theirs in Chicago who was an attorney.