I agree about requiring a re-homing fee.
Too many teenagers looking for free cats to do bad things to (an over generalization, I know). I think a fair re-homing fee for kittens is $50-75. This is not unreasonable. It won't deter a good pet owner from adopting and helps the rescuer (whether it be a group or someone who just found the poor animals) recover some of the costs they have spent on the animals. Nobody is making $ off of an adoption fee. When I adopted Matilda , she was $75 and that covered her micro-chip (she arrived at the shelter already spayed/neutered but they would have done that too). She was up to date on shots. Chloe was a kitten (12 weeks old) when I adopted her. She was $50 but not spayed/neutered and not micro-chipped. She was up to date on shots and they gave me the rest of the vaccines to do myself because they get them at cost. (I didn't end up doing them myself though).
You can't let them go to a new home without being spayed or neutered. I realize that $ is an issue so here are a few different ways to go about this (most have been mentioned, some haven't I don't think). Only about 1/2 of potential adopters are going to spay/neuter kittens, which means that if you don't take care of the issue now, there WILL be future kittens. Then the problem just repeats itself.
1. Pay for spaying/neutering before advertising the kittens. The $ will partially be recovered by the adoption fee of each kitten. This is the best option, but if you don't have the $ to do it, then that's not viable. I don't think you need 2 weeks after spaying/neutering for the kitten to recover. Females might need more recovery time, but even then it's not 2 weeks. I would keep them as long as they are on antibiotics, but invite people to come see them in person before they are ready to go (remember, the smaller the kitten, the easier to adopt!).
2. Relinquish the kittens to a shelter. Offer to be a foster home for these kittens through the shelter if they are worried about space. Explain the situation you are in and how important to you it is that they be spayed/neutered. You might be surprised on what they can do for you. Kittens are relatively easy to find homes for and shelters know this.
3. Ask adopters for the adoption fee of say, $25, and then a REFUNDABLE amount of money (say, $100-150) that you give back to them upon proof of spay/neuter surgery. The problem with this is that not many people are going to be comfortable doing this. I've seen shelters do this, but that's different than some random unknown person.
4. Have them pick up kitten from spay/neuter surgery at the vet (that they pay for).
As for as an adoption questionnaire, ask them to e-mail it to you before they meet the kitten so that you don't have to make a decision while they are there in person. Good questions to ask (I took these from an adoption application I'm filling out for a dog)
1. Name of Adopter(s)
2. Address (and if renting, proof of landlord's permission for cat(s)).
3. Phone Number
4. E-Mail Address
6. Is anyone in your house allergic to cats?
7. What are the requirements for cat owners in your community (i.e. number of cats allowed, vaccine requirements, etc.)
5. Where did you get your pets?
6. Where are they kept when you are gone?
7. Are they up to date on vaccines?
8. What do you feed your pets?
9. Name and Telephone Number of Current or Previous Veterinarian
5. How long did you have him/her?
6. What happened to your pet?
7. Have you ever sold, given away, and/or surrendered a pet(s) of yours for any reason?
8. If yes, why?
1. Why do you want a cat?
2. What circumstances, in your mind, justify getting rid of a cat?
I would also print out sheets on helpful resources for cat to cat introductions, dog to cat introductions, litter box problems, food recommendations, and an article about Soft Paws or something like that.
Oh! And make sure everything is done in cash (not check).
When placing an ad for the kittens, have you decided where you will do it? I would start at vet offices (and include pictures on the ad), PetSmart & PetCo (if they'll let you), and then go to the Petfinder section that lets you put up adoption listings if you aren't affiliated with a shelter/rescue group. Also there is craigslist (provide as much information as you can about where the kittens came from because you will get a lot of hate mail if people think they are from an unspayed pet that you have).
I kinda wrote a lot
Best of luck!!