I think whether PA or PI would depend on the size and usage. Thus for a small organisation it will be ideal to get a PA and for a big organization it will be ideal to get a PI

its going to depend current situation and also provision for growth. Typically a /32

I f you run out space you will have to apply for more. You might get the next block in continuation from the old or you might get a totally new block

The question is not clear, can you please give more context

Please clarify the question, give more context

20 bytes but however can reach 60 bytes