Was mercury used as a preservative in vaccines, and if so, in what doses, and is there any evidence that this caused increased numbers of neurological/psychiatric disorders?
Yes, it was. I don't know what doses, but for the last question, the fact that autism cases didn't drop after they stopped using it suggests that it wasn't what was causing the recent increase in autism cases.
The mercury that used to be used in vaccines was only in trace amounts. It was added earlier in the production process to prevent bacterial growth, but then the whole lot was much further diluted for working concentrations actually used in the vaccines.
There is no evidence that it contributed to any neurological/psychiatric disorders when it was used.