1) Washington believed that " [Political parties] serve always to distract the public councils and enfeeble the public administration. " He thought that they were just a way to start up unnecessary fights and create illogical or unimportant problems. He also knew that they agitated the community and created jealousies and makes foreign influence and corruption more common.
2) Washington believed that trading with foreign nations was enough, and that we didn't need to discuss politics with them, for it could lead to unwanted complications. He also said that the agreements they had previously formed together were good, and that they shouldn't make any more plans, in other words, play it safe; he didn't want a war or argument on his hands.
3) I honestly think he was so cautious because he didn't want conflict. He just wanted everyone to be content, happy, and safe in America.
4) I do think that his concerns were valid because political parties have created all kinds of problems present day. We've had disagreements, protests, riots, violence, and destruction due to the differences in the parties' beliefs.
5) I think that his predictions were right AND wrong. Foreign trade and agreements have help our country on many accounts but they have also caused many unfortunate misunderstandings.