Compared to World Warfare, main accounts have a bigger impact in Heartlands Clash, with the impact of sub-accounts limited to reducing Morale, total ATK and HP. With a fixed number of battles, the kill ratio of your main force is an important benchmark for tactics, with a lot of trial and error involved.
Region Selection
Only alliance leaders/deputies can choose the region to start in. There are 4 regions and 8 randomly matched divisions per week. Taking into account increases in alliance members after the merge, the 8 divisions represent 8 main alliances, with some divisions possibly having a second alliance.
Division champion determined from Tue to Fri (can gain vassal or associate alliances during this time)
Heartlands overlord determined on Saturday
The choice to make is which region gives you the most benefits. There is only one overlord reward per region, and there are the finals on Saturday, so region strength is an important benchmark. Alliance and vassal strength are also important for determining the final winner. In the above image, for example, there are three main alliances in Bashu, so they will go into the heartlands together. When there is only one alliance in another region, the 3v1 battle will likely go to the region with more alliance (not sure about the high BR conversion ratio).
There are two questions to make clear however:
1. How many rewards do vassals and associate alliances get (from auctions etc.)
2. Whether the overlord reward is available to vassals and associate alliances (including heartlands reward)
Question 1 concerns the final region choice. If vassals or associate alliances do not get benefits from the main alliance, alliances that do not have designs on the heartlands should go for a weaker region to claim the overlord reward. For question 2, I feel that the region's overlord reward will not be divided evenly, while the final heartlands rewards have a high chance to be evenly divided, because alliances that have contributed should be rewarded.
Deployment
Battle mode starts after entering a region