You need to read more. The Russian declared war on the last possible day they could, according to their agreement with the allies. It had nothing to do with Japan's condition. Japan's whole war strategy depended on having their entire force in the South to defend the home islands against the U.S. They had no contingency plans for defending from Russia in the north. They knew they'd be screwed if Russia attacked the homes islands.
And Russia DID invade Japan. They were kicking Japan's butt it Manchuria. Japan had over 80k dead and 650k POWs.
Japan did not rush out and have a Supreme War Council after Hiroshima. They waited three days. And then they moved the time of the council up, after the news of Russia's declaration of war and invasion. So, Japan did not attack with absolute urgency and panic after Hiroshima, but they did after the Russian invasion. (I am not arguing that the nuclear bombs shouldn't have been dropped; just that it was the cause of surrender)
Russia then grabbed as much territory as they could before the war ended.
Russia, didn't, "grab up," as much territory as they could. Those territories were specifically promised to Russia by the U.S. and the U.K. if Russia agreed to declare war on Japan
The Russians knew we had the A bomb almost as soon as we did but did not declare war on the Japanese because they feared them.
Again, read up. Russia had a neutrality pact with Japan, and FDR/Truman stupidly let them keep it in place. By the terms of Yalta, Potsdam, etc. the Russia were required to declare war on Japan exactly three months after Germany surrendered. VE Day was May 8th. Russia informed Japan they were declaring war just before midnight on August 8th and invaded Manchuria at midnight. Japan was desperately trying to extend the neutrality pact for months before that. And Russia tried to give them hope it was possible.
How exactly were the Soviets going to get an army onto Japanese soil when they had no ability to do so?
Russia only declared war to seize whatever they could. The Japanese were still holding large areas of Manchuria after the surrender. The Russians had not even come close to invading Japan unless you think taking a few isolated islands as invading.
Russia agreed to join the war at Potsdam and the reason is they knew we had the bomb yet they still waited until the last minute. They did so because they still feared Japan at least until we destroyed them.
The USSR behaved in their usual way. Taking what they could after the Western allies had broken Japan.