Hi Jason,
Are we going to get reimbursement for the printing fees? If so, how is
the process of getting it? Additionally, is it better to create a
month report of our spending and ask for reimbursement at the end of
the month, or ask it as soon as when we spend money?

If there is an event that you would like to represent Fedora at and you would like money from Fedora to pay for event materials;
then you will need to request a budget for that event from the Fedora Ambassadors Steering Committee.

You should also make sure that this event is listed on the FedoraEvents page:
http://fedoraproject.org/wiki/FedoraEvents

As to the exact procedures for submitting receipts, etc for the event money, I am not sure what they are.
Hopefully, someone more knowledgeable on these procedures can explain/document that.

Additionally, as an Ambassador, do we get assignments of the events?
Or we decide on what events we're planning to do?

No, you are not assigned to an event. Rather, sometimes there are events listed that don't have an owner but is looking for one. Or if there is an event that is not listed, that you would like to rep Fedora at, then feel free to add the event to the FedoraEvents page with yourself as the owner.

--Jason