One of the challenges of planning a multi-month, multi-country trip is figuring out how much time spend in each region/country and what the best time of year is to visit.
Travel Tip: Lonely Planet offers free, online access to the Getting Started chapter for each of their guidebooks. In addition to providing an overview of the country, its history, and culture, the Getting Started chapter also covers the three most important trip-planning topics: when to go, costs & money, and sample itineraries. Use this information to determine the best time to visit each country and how much you should budget in terms of time and money. This will allow you to develop a good, overall sketch for your trip. Once you have this established, you can then dive deeper into your trip planning.