There are a few other factors, but yes, it's safe.
yes
no it is not
Yes
Yes. I have done it more than once.
Mod Loader is the only mod that will allow your client to run more than one mod at once. It is very safe!
Yes & no. You can, actually, get mono more than once. Although not many people get it twice, you can & people do, so be safe regardless.
It can occur more than once.
You can be be exposed to it more than once
yes. enzyme can be used more than once
Yes, you can have LEEP more than once.
It is safe. More than 70% of the atmosphere is nitrogen