My point is not so much that America doesn't have an impact on other countries... rather this is much bigger than any one person. There is a lot of checks and balances to our political system. People thinking things like "all my god Trump will destroy the world" or "Trump is Hitler" is asinine.
As far as what Trump says, I agree he can sometimes spout things bluntly when they could use more tact... however, a lot of people agree with him or in part. Him having "very little actual knowledge" of those issues is simply your opinion (which is probably formed by the biased media that always like to share their views).
Presidents learn on the job... and so will Trump.
You're right that congress has power too, which used to be checked by the president until today. But most of congress' influence is domestic and while we feel kind of bad for you when Ryan and his pals dismantle the social safety net in order to give the richest 1% a big tax cut, it doesn't really affect the rest of the world directly. A lot of the foreign stuff is handled by the executive branch though, now in the hands of someone who probably'd have trouble telling the difference between Chile and Peru.
Trump not knowing that Russia invaded Crimea or being unaware of what the First Strike principle in nuclear policy means isn't an opinion. It's a fact. People asked. He didn't know. It's that simple. People learn on the job, if they're intellectually curious and are willing to learn. Trump couldn't even be bothered to study for his debate performances.
It's popular to say that both candidates were equally bad. They used to say the same thing in 2000. I'm pretty sure quite a few people wished the supreme court had broken the tie in Gore's favor in retrospect.
Also, foreign policy isn't just about how much to be involved with other countries' business, but also about how much to stop being involved in other countries' business. In the latter's case, walking out of international treaties or alliances, potentially leaving vacuums for others to fill.