Good idea to do at the same time
Not necessarily. If the car was in alignment prior to getting the new tires, it will be in alignment after the new tires. It isn't a bad idea to check the alignment periodically and it is probably better to check it more frequently than when you get new tires.
new tires does not mean you don't need alignment. it is always a good idea to have the vehicle aligned after new tires are purchased to avoid premature wear, even if the car shows no sign of mis-alignment.
No. If there had previously not been any alignment issues, and as long as the new tires are properly balanced, you will not need an alignment.
No, not as long as normal wear pattern on the old ones.
Yes, alignment can be done either way.
There is no need to have a cars wheels aligned on a regular bases. It is a good idea though to have the alignment checked when installing new tires to prevent excess wear on the tires.
You could, but it would be more accurate with new tires.
I'd at least have it checked, just to be sure everything's fine
they are not always required but if the old tires had an odd wear pattern it would be in your best interest to have an alignment