As a worker, yes, you got paid in rubles. However, it should be noted that often times you would not be able to find goods to buy with this money unless you had "blat", or connections with people who would enable you to find scarce goods.

Yes, there were bank accounts, they are of course, in banks ran by the state. The Sperbank, which was a subdivision of the GosBank (the Soviet central bank), handled all household savings. You would have had an account with the Sperbank.

Could they negotiate their rate of pay

Under Stalin, the vast majority of workers were paid a fixed amount based on your output, so if you were a factory worker, you would be given a quota and then you got paid based on how well you fulfill your quota. A miner would be required to mine a certain amount of coal for instance. If you overfill your quota, then you get paid more than your base salary. If you truly over-performed then you would be celebrated by propaganda as a "shock worker". However, if you under performed, then you got your pay deducted, or worse.

Was there any sort of investing?

By the state yes, you would be often forced to save a large portion of your earnings inside the Sperbank, which would then come under the planning bureaucracy which would direct where your savings would be invested in.

As for personal investment, Marxism have an ideological prohibition towards "private ownership of capital" which means you cannot buy shares in a firm, there was also a belief that interest rates are "exploitation". Hence, you would not be able to do personal investment.