Hello,
1. request details per project
Here you have two possibilities:
a) as API v18 does not provide a possibility to fetch requests using the PROJ endpoint, you need to use the endpoint OPTASK, which is the one for issues / requests.
https://instance.my.workfront.com/attask/api/v18.0/optask/search?projectID=<projectID>&fields=*
b) alternatively you can use the (unsupported) internal api, which allows using the endpoint PROJ:
https://instance.my.workfront.com/attask/api-internal/proj/<projectID>?fields=issues:*
Concerning 2 you need to be a bit more specific.
It is best if you familiarise yourself a little with the API Explorer.
3. Getting custom form field values
Field values from custom forms are stored in the collection parameterValues.
https://instance.my.workfront.com/attask/api/v18.0/optask/search?projectID=<projectID>&fields=parameterValues:*
Regards
Lars