1. Try the settings at File -> Options (all the way at the bottom under 'Account') -> Advanced -> then uncheck "Use system separators". It will then allow you to specify the character to use for thousands.
2. You can change your region within the control panel to have the currency be dollars by default but it's simple enough to click the dropdown when choosing the currency format for the cell and choose dollars. If there are many cells you can use format painter to spread the currency format.