Had the Japanese thought they could have gotten away with attacking solely British and Dutch possessions, they would have done so. However, the geopolitical climate of the time strongly suggested that they wouldn't have been able to - the US was taking a strong stance against Japanese expansionism in China. Making an attack against European powers the US was being friendly towards would, in the view of Japanese strategic planners, ultimately result in the US entering the war. This was highly dangerous to Japanese plans. The main sea lanes between the Japanese targets in Malaysia and Indonesia and the Home Islands ran past the Philippines. The Americans were, in 1941, in the process of fortifying them, and turning them into a major air and naval base to attack these sea lanes if necessary. Allowing the US to complete this work would preclude any Japanese expansion in Southeast Asia. Therefore, the Japanese had to attack the Philippines, in addition to the resource-bearing areas of Malaysia and Indonesia. To forestall any response to this from the US Navy, various Pacific islands had to be captured, allowing the establishment of a strong defensive perimeter. To allow this, the US Pacific Fleet had to be temporarily neutralised, hence the Attack on Pearl Harbour.

As to your second question, it was unlikely to change much. Malaysia and Indonesia (and to a lesser extent, Burma), fell quickly without requiring the troops used in the Philippines. The campaign in Northwest Burma and India was not part of Japanese strategy, but was essentially a campaign of opportunity. The troops used were either not needed for other plans, or were earmarked for plans for which shipping could not be found. Adding more troops earlier would simply have strained supply lines, and would not have resulted in a worthwhile success.