That is correct The column you have highlighted is 'Working Set Delta', which is change in working set memory. To add/remove or change this to the correct column, right hand click on the column title area (such as where it says 'Working ...', then select columns. A list of items with checkboxes will appear, most aren't selected. Uncheck the box for 'Working set delta', and select 'Working set (memory)' instead. You can leave the working set delta column there, but there isn't much point. You can add other columns like CPU time etc.
That's correct, they all seem about right. You also have private and shared memory sets. Those listings are for the total memory of the app, including shared. You could set shared as a separate column. For instance, Firefox says around 200MB in that screenshot, but 30MB of that might be shared with other applications. If you close off Firefox, you free 170MB of RAM.