Some ideas from my years of putting together concerts and festivals:

Get sponsorships from local businesses or corporations
usually in exchange for advertising they will help with expenses.

Pay the musicians and assure that they will be able to travel
to your event. Provide them food and drink .

Offer free entrance into the event to folk who are willing to volunteer (take tickets, provide information, other staff positions)

Is this event one that people will pay to attend, or is the city or
county footing the bill so it can be free to all ?

identify different people (staff, musicians, audience, vendors, etc)
by colored wrist bands. that way those with access into different areas will be easily known. (some may have multiple wrist bands)

if people are bringing their own chairs for seating, you may want to
determine a height requirement so tall chairs do not block the view.
(short chairs in front, tall in back)

Determine whether you will be doing recording..audio or video of the performers, and plan permission forms to allow this if so.

You may make contact with your local Public Access Television station
or college training facility where video production classes occur
to see about arranging to invite a portable/mobile production team
to create archival footage of your event, with possible broadcast on public access television or Public T.V. (P.B.S.) station.

Make contact with the local historical society to document the authenticity of your program and or performers if historical accuracy is part of your goal.

check out this festival...a very successful and long running event
www.strawberrymusic.com the Strawberry festival happens twice each
year and they have learned how to produce and present this event.

have fun!