This is coming from a guy who doesn't have a lot of experience with 6-man football, but I proposed 6-man football at Campbell and put the information together to get them to start football. The toughest part was finding a place to play because we couldn't easily play at TAMU-Commerce or another high school field because of the difference of set up. Fortunately for Campbell their baseball field was just large enough to fit a field into the out field. Unfortunately I have moved on from Campbell and don't get to see the new excitement about their football team. This is coming from a school administrators view point and someone who presented information to a school board about the expenses of having a football field, I will give you my views.
1. Call the schools that you think may use your facilities as their home field. Let them decide if they would play there and then build around their specifications. If they could play at your facilities for no fees any school would go for that. It should be more cost efficient for the schools. I wish more schools that were in close proximity would do this, less cost for the schools and nicer fields. The large districts with multiple high schools do this. When I lived in Edmond, OK three high schools and a college all used the same field.
3. Locker rooms, parking, press box, and seating capacity would be the biggest concern for a playoff venue. The largest expense you will be looking at will be the lights, locker room, and bleachers.
4. If you want playoff games and multiple schools using your facilities, I would think a nice press box would be a must. When I say nice, several rooms two for coaches, one for scouts, one for media, and one for timer (five total) and a balcony for schools to film. When I say nice, I just mean the space, it can be built with metal/tin/wood (I'd insulate though). Windows and AC is a MUST, but you can just put AC window units in each room on the back of the press box.
5. I don't know about size, but I would go with four locker rooms so you can play two games in one night and start the second game soon after the first. You don't want to have to wait for one team to get out of the locker room before the next team can even start to get ready for the next game. Anywhere from 2 to 4 coaches.
6. My thoughts on the concession, have your parks and rec do it. You will raise a lot of money, but then again your schools that use it for a home field may want to do their own concession.
7. Yes, their are many Saturday afternoon games and I think it may be because of the light issue. I'm not sure what the electricity cost is to run the lights.
8. Don't charge your schools to come play. If you do, they won't come. Tell the schools they use your field for free. The Parks and Rec will collect gate and concession. The Parks and Rec will pay the officials out of gate and concession. You may not get to dictate gate as some districts set a gate fee for district games. Charge schools though if it is a playoff game, all regular season is no charge.
I ran the youth league last year at Campbell too. We played at Lone Oak's old field. We brought a trailer for concession. We had three games a 1st-2nd grade game, a 3rd-4th grade game, and finally a 5th-6th grade game. After paying $425 for officials for all three games we profited anywhere from $800 to $1200 each weekend. Our gate was I think $3 adults and $2 students. Obviously for high school games you will charge more. Our concession prices were relatively cheap too.
I think you would be talking a good estimate of $750,000 and that may be a little low.