You really won't be able to buy anything in January that you won't settle on until June. You should do your househunting online, by driving through neighborhoods and by visiting open houses, until about 3 months before you'd like to move....then it makes sense to start seriously looking. Until then, you are a "tire kicker" and not a buyer, and a strong buyers agent is busy with people who are buying. We often work with people online and over the phone - coaching them through the process, sending listings (usually automatically), introducing them to lenders, sharing market information for months prior to getting into the car with them. For that reason, it is good to start working with an agent (or two) ahead of time. I would not sign an exclusive agreement for this "early education" period - this will give you an opportunity to learn about their skills, follow up skills, communication styles, etc. so you can chose an agent you enjoy and trust. This is a big deal and you need to have an agent that really does care about you. There should be no fees for this service. Plus, doing it this way will ensure that you are well educated when you actually do start looking, and you'll be able to move at the speed of the market.
Agents generally get paid when the home closes - unless you are looking for a needle in a haystack, and then there may be up front fees.
Good question and good luck!