cleaning outside glass

I wouldn't put any type of glass cleaner on or near the tank. Most of them contain chemicals such as ammonia and other nasties.
I use straight vinegar and a paper towel. Being doing it that way for a couple of yrs. I also clean the salt creep with vinegar on the paper towel. And soak the skimmer and phs with straight vinegar.

I spray windex on a paper towel somewhere away from the tank and then use the paper towel to clean the glass only. Is this okay? I have not had any problems for years. The important thing is to make sure no windex touches the water.

There is a glass cleaner specifically made for cleaning aquarium glass. It's non-toxic to fish and can be found at your LFS.

The safest is probably just water...