Select right interns and leveraging them to the fullest

Hi there, I'm looking for some guidance on the following? Would someone with this experience be willing to chat for a few mins? I'd really appreciate that.

a) what types of interns people have had success with for data gathering, market / industry analysis, data analysis, etc. (e.g., full time vs. part-time, undergrad vs. grad, finance/econ vs. liberal arts, paid vs. unpaid.),
b) how many interns did you need for the work?
c) how did you leverage interns over the course of time, esp. part-timers (daily rhythms, accountability, motivation)?