I am going to install recessed lights in our outside Church Pavilion. The ceiling size is 24' x 36'. Using 8' centers I calculate, along with 2 -54" ceiling fans, I will need to install 17 -75 watt halogen lights to illuminate the area. I will have approximately 125 lineal feet of wire from the switch source to the fixtures.

My question is:

Will a 20 amp circuit breaker with 12 gauge 12-2 w/ground romex wire be ample?

Thank you so much!

17 X 75 = 1275 Watts, No Problem.
1275/120=10.625 Amps
I could be wrong, but 1000 Watts may be the largest dimmer in a single gang device.
You might consider having on 2 switches, every other light, or in rows, so you can use smaller dimmers and/or cut half off to conserve electricity when not needed.

He never said how many dimmers he would be using, if any. I have a 1500 watt one myself.

Consider using Northwest Envirofan Agrifans for your outdoor fans they work GREAT and are much better for the price.

I hate to be the voice of reason here, but are you aware of the codes involved with wiring in places like churches, meeting rooms, auditoriums, etc? Do you know what "place of assembly" means? Do you know the wiring requirements?
Are you also aware of the extreme liability issues involved? What if you screw something up? Do you have the proper insurance? What about your conscience?

If you have to come here and ask these questions it is obvious that you are not a licensed professional. I know churches are a touchy subject. Everyone is always trying to help, problem is not every one is qualified to help, and the powers to be rarely turn down free help such as this.
Don't get me wrong, I do a LOT of gratis work. Difference is I stick to what I know and what I am qualified to do. If someone asked me to put in a new boiler I would even consider it, I'd call one of my plumber friends.
If you are not doing this for free and are charging them it may even be criminal.

Once I saw "Church" in the first post, I immediately thought "place of assembly".

I should have known, Stan caught it already, and rightfully so.

This needed to be comented on, as this is a serious issue.

I will say thou, if the space is rated for less than 100 person occupancy, then it does not need to be wired per Article 518 of the NEC, Assembly Occupancies.

Romex is not allowed in a Place of Assembly.

I do pick up on a another issue, the word "Outdoor".

I bet your going wonder why you asked questions here, because your going to get slammed again.

"Romex", typically being NM-B cable, is only rated for DRY locations. This Outdoor Pavilion may be considered as minimally Damp location, therefore, again "Romex" is NOT allowed.

Everything else Stan mentions I agree with. While donating time, labor, etc for a charitable organization is commendable, performing electrical wiring must still be done within all the rules, laws, and regulations, ESPECIALLY, a Place of Assembly.

Licenses, permits, stamped engineered plans and specs, all have their purpose.

Even if a licensed person does a job in a Place of Assembly without a permit, is a criminal offense, in at least one state that I know of personally. ( No I am not referring to myself, nor a "friend".)

So, unfortunately, you asking what size wire for the 17 fixtures left you wide open as DIY'er, and not a professional.

You need to go back to square one, and get a professional to help with this installation, not only for your good, but the safe custody of the occupants of this church, even if the occupancy rate is under 100 people.

Yeah, what they said!