Is this possible with EE 1.6?
1. Users would be able to register and place adverts which would expire after a given amount of time (they could choose how long). The adverts would consist of photos, body, title, dates.
This is possible, they can set the expiration date to say how long it would stay up.
2. The adverts would only be shown once a paypal payment has been made to the administrator. Adverts would automatically expire after the listing period paid for.
In EE you’d probably approach this differently, giving them access to post after purchasing an item that changes their member group (from one without posting privs to one with posting privs).
There isn’t an out of the box way to tie an entry expiration to a listing period - with the Simple Commerce module, you make a purchase and that’s it. Beyond that would require a custom solution.
3. The user can see all their active and past listings in their profile and relist if necessary (with another payment).
This would take customization.
I have used EE a few times but never used the membership module (I have only used the free version) so don’t know what kind of features it has.
You can access the member permissions in EECore - EECore simply does not allow front-end listings.
Also how hard would paypal IPN be to implement? Could I write a plugin to do this?
The simple commerce module can handle the IPN side.
Ultimately, the payment system - listing what was purchased, handling that entire side other than the initial purchase would need to be a custom solution using our Development API. I’m not sure if FoxEE could help you but it may be possible, and worth a look at.
You can always try out the full version using the 30 day hosted demo.