How effective would sanctions on the US by the international community be?

Right now, it would likely harm other countries at least as much as the US. We're just too interconnected into every aspect of the global economy. Cutting off the US cuts off a lot of services that other countries rely on.
But, Trump's current foreign policy is driving countries away from the US fast. Give it a few years for countries to disentangled themselves from the US and it would likely be more effective without harming themselves in the process.

Depends on by whom and how long. The US produces a lot of things but also imports a lot of critical goods and materials as well.
If Canada, Mexico, China, and the EU & UK all banded together for sanctions or embargoes? The US economy would be pushing daisies pretty quick. Especially if the actions were coordinated and did not give the US time to react and adjust.
But the countries issuing those actions wouldn't be in good shape either. Trade wars are a 2-way street.
- Why would anyone bother with sanctions? Nothing a foreign government could do would be worse than what our own is doing.
  Just wait it out and hope you manage to find a way to secure our nukes after everything disintegrates.
  
  To encourage the revolt of the increasingly dissatisfied American public.
  And for those who say "that's not going to happen", you do not speak for the rest of us. There is absolutely unrest. The news cycle does not reflect reality.
- Would also depend on how captain dipshit responds. This could be interpreted as an act of aggression considering he and his cronies are itching for a reason to invade somewhere
  
  All talk.
  Been around plenty of disordered folks and he fits a very specific bill.
  He's chickenshit. Lotta threats but won't follow through. His reputation is everything to him, but he will absolutely turn tail and run if he is challenged by a more powerful opponent. He will absolutely hold a grudge and try to get revenge in a """sneaky""" way, but he's still an absolute fucking idiot.
  
  Anything is an act of aggression with them. The only tong you can do that they won't call an act of aggression at this point is rolling over and giving them your country.
  It's abusive tactics 101, the only way to stop the abuse is to do the things they don't want you to do, even if it gets worse first.

I think aiming to sanction the US is the wrong plan, treat it like it is what it is - a country run by an autocrat, and go after the oligarchs. Same approach as taken with Russia, North Korea, Iran, etc.
In terms of effectiveness. Frankly we're (globally) only getting rid of Trump and his cronies if the American public rise up against him and oust him through whatever means that may take. Protests and extended strikes for starters - and the people will be more likely to band together with Trump than against him if the whole world starts Tariffing and sanctioning the USA like a rogue state.
On the other hand, sanction and freeze Trump & Co. assetts all over the (western) world and when he retaliates to protect his own interests its a lot harder to sell to his constituents.
How you would even legally go about that is another question though, he would have to be breaking financial international laws and the countries involved in the personal sanctions would have to be ready and willing for blowback.
Its all fantasy at this stage until he starts blatantly breaking international laws that allow his assets to be seized. Likewise with the idea of US sanctions - look at how much Israel has done and they're not sanctioned, and it took a great deal of blatant acts of war before Russia and North Korea were sanctioned also.

yo gonna ban swift from swift? lol where do they grow you?
- SWIFT is headquartered in Belgium.