Edited to remove unneeded quote.
We do weddings/receptions here, anything from a small eplopement to 100 max. For receptions 40 or under we are able to do inside or out, larger events are outdoors only and we do not do those during our hot summer or colder winter months even if begged and pleaded with.
First (as others mentioned) check your zoning, ins. etc. Since you mentioned a DJ, ask about your city/county noice ordiance and requirements concerning gatherings. (The law here states we must have a officer on duty for a gathering of 75 or more. I must pay for a min. service of 4 hrs @ currently $30hr.)
Weather is a factor: While we do outdoor events, we have a covered pavilion with a floor which provides plenty of space (could seat 150) so if there is a hard rain, they still will not get wet. If you are using tents, make sure the tent company has the sides and floor that can be added to the rental if it is predicted to rain. Since you mentioned DJ, be certain to include a rental dance floor.
CATERING & CAKE: After a trial and a learning curve, we only do wedding/reception packages. I have a caterer (and a back up) and a bakery that I use exclusively. NO exceptions....I have a few horror stories that would make even the most trained wedding corrdinator go ballistic. I will not bore you with details but will say that I had more than once - they hired a caterer or bakery I approved, then later canceled and hired a friend (no experience, no license). Each time I was not made aware of the change until a few days prior when I called the caterer to arrange set up etc. Of course the owner (the caterer) would have called me if they had known, but each time it was an employee that took the cancellation so it was gone unnoticed. Another REASON for this: While the Brides/Grooms families may know where they purchased the food, drinks, cake etc.... the guest DO NOT - they are under the impression that the facility provided these things. If the food is bad or there is not enough, the cake is a flop, etc.. it is a reflection on YOU and YOUR B&B.
Out door restrooms: We installed our own, nicely built and very well maintained outdoor restrooms (they are like the nice portable restrooms). Some of the female guests REFUSE to use them - flatly! We do have a general use bathroom, and just had to go ahead and open it up to their use. Again, another reflection on your place!
Rooms: We use to require rental of all guestrooms with the wedding, now we just block them off for the night, and include our nicest room for their honeymoon night. Another is used for the bridal dressing area. (all our rooms are on the 2nd floor and we rope off the stairs) We did this because it was easier on US, we do not have staff for the B&B (we hire wedding staff) and trying to clean the rooms, prepare for the wedding, tend to the brides needs etc. is far more than we can do in one day, plus then getting up to prepare breakfast for a full house is just TOO much. If you have staff, you may consider the room rental as a requirement. I would not have NON-wedding guests be overnight guests, they would feel out of place and would not experience your B&B as you normally describe it. NOTE: having the rooms required for rent also opens the house to be trampled in by others because there are always those that just want to 'take a peek - I am sure you won't mind'.
Time allowed: I allow 30 minutes for the wedding, and 3 hours for the reception. My weddings must conclude (if outdoors) by 10PM. I also allow a 30 minute rehearsal time the day/night before. (side note: stress only Bridal party, parents ONLY for rehearsal or everyone and their brother will come and add their 2 cents....) As stated you will also need time prior /after for set up/breakdown.
You did not mention this but what about liquor? A lot of people what it at their reception. If you do not have a license, check the law to see if they can hire someone to come in to handle this that has one. This is what we do. Our packages are NON-Alcoholic. If they want to hire someone, we have a list, they must book it themselves. I also have the bridal family sign a seperate agreement of Indemnification as well as their contract. NOTE: if anyone other than one of my approved bar companies would come to set up, they would be turned away and the reception would be soft drinks & tea only. This is stated FIRMLY to them. It is funny, I never had anyone try to skirt this policy, yet they did with the food...you can tell where their priorities lie! Also, I always hire (and add to their bill) a security officer if alcohol is going to be present.
Finder's fees: I do not expect one, nor do I give one. I would rather the friendly word of mouth advertising exchange. This is my ethics talking. I prefer someone referring my business because it is a nice place, not because they will get a monetary thank you. I do have a couple of photographers that I recommend and they have done some really nice things for me as a thank you (as well as the word of mouth).
Music: DJ's - personally I hate them, even the most professional! They always are requiring more electricity than they state when we discuss the need. They do not listen to US about how loud they can play. (they think because it is outside, the sky is the limit) I would prefer a small band over a DJ, don't know why but never had a problem with a band. MY preference is to have canned music. We have a surround sound system and we discuss the music choices with the bridal party. They can either select from our selection OR they can bring their own CD with the following restrictions: require the music to be played in the order they record it, and that there is NO vulgar music played (this is for any music - DJ, band or CD). I just remind them that a wedding is an elegent event, not a party.
Cost: This is something only you can decide. Things to place on your detailed list: Costs of all rentals, room revenue loss (or included), YOUR time - once they book to arrange rentals etc.; day before for deliveries, set up, rehearsal; ALL day wedding day; break down/ cleanup time. Make sure you have have a security deposit (refundable if all is back in order). I collect payment in increments in a payment plan NOTE reall bold your policy for canceling and you may consider adding something regarding inclement weather but be very clear.
Receptions inside: as a note, we have several places in our area that do indoor wedding receptions. They open several rooms for the event and people wonder around. I personally do not care for this as I have missed things like cutting of the cake, etc. and makes socializing more dificult, but others really like that atmosphere. Just throwing this out for you to consider incase you haven't. (I don't know your layout).
Feel Free to email me personally if you want more details on anything.