TEMP tablespaces should not be set to AUTOEXTEND; they way that they work is that they don't free up space unless needed, so if you set one to autoextend it will just keep on growing & growing, whereas if you don't then when it gets full it will automatically free up space that is no longer needed. (This means that after it's been used a while it will show as always being full or very nearly full - you can safely ignore this, as it's a quirk of how the TEMP tablespace works.)

I can't think of any good reason why each user should have their own TEMP tablespace, but I guess it depends on the design of your database...