Second hand cylinder

Hi

I've just bought a second hand cylinder and I have a few question I'm
hoping someone can answer.

The cylinder is a 12.2 liter which has been O2 clean and was used for
nitrox, what I'll like to know, will there be any problem filling this
tank with normal air as that's all I want to use it for.

The cylinder had a Nitrox sticker on it which I've remover, and its the
old yellow colour, it has been hydro test this year, and has all the
right sticker, and stamps on it, will I need to replace the nitrox
sticker with anything else.

How often will I need to test the cylinder and what will it need testing
for, currently it doesn't need to be tested till 2009.

One final point, how long can a cylinder be filled with air before, that
air is not usable or doesn't matter.

Thanks for any help.

Darren