Can I use Mechanical Turk for a longitudinal study? My thesis looks at depression and social support. My design involves participants answering taking a survey every other day for a total of 10 times. Is is the same set of questions that they will answer each time, but I need to see how the responses change over time.

1) Is it possible to set up such a 10 part study on Mechanical Turk, where they will have to return every other day to take the next part?

2) If yes, will have to pay them as they finish each part, or can I pay them when they finish the whole study? I was also wondering if it might be possible to pay a bonus amount to those who finish the whole study - as an incentive to keep coming back each day. 

2a) How much should I pay them each time? The survey consists of 23 rating questions on a 5 point Likert scale. I tried it and it took me a little less than 4 minutes.

3) Also, is it possible to accept their answers but only pay the ones who finish the whole study? Because I will be discarding the participants with missing data from my study anyway.

4) The survey results will be anonymous but it is a diary study of sorts. So, I need to be able to connect participants' responses from one day to the next. Will Mechanical Turk allow me to generate a specific code for each participant? Or does each worker already have a code?

5) What survey platform do you suggest I use for setting up my study? Will google docs work?

6) I read somewhere that Mturk workers don't like giving out their emails. But I need to be able to send them emails everytime the responses are due. Will Mechanical Turk allow for this?
The best way to set up a Mechanical Turk longitudinal study is with TurkPrime.com. You can follow-up with users and invite them to take a new survey. As long as they are properly incentivized they will come.

I recommend that you inform them at the start that you are running a 10 part study and that those who perform well on each of the 4 minute studies will also receive a significant bonus, say $5-$10.

See here for some more instructions on setting this up.