It seems there is a big difference in foreign policy of Buddhist countries before and after the 10th century. Therefore, I should stop limiting the "crusade" only against Muslims and should also include Hindus- so that it can be before the 10th century.
Of course, there are major obstacles for this to happen, some of which I can identify are:
1. the Strait of Malacca is probably controlled by a Hindu government, which means it needs to either be circumvented or attacked. (in retrospect, this can get very interesting.)
2. there needs to be a central religious authority (and/or a regional Indian Buddhist government) that calls for action because of an attack.
3. the technology of the ships need to be in capacity to carry large amounts of people across a large expanse of water(Indian Ocean and South China Sea).
4. the Buddhist regional government that (may/may not) control the "holy areas of Buddhism" needs to logistically support the attack. Otherwise, it is impossible to go all the way into Northeast India.
please add to the list if you can find any other difficulties that have to be overcome to have the Buddhist Crusade!