I have interviewed with both big Pharma and Publicis. The interview is pretty much the same, regardless if contract or not. Most managers that work with Publicis have come from big Pharma anyhow. Interview as you would for any pharmaceutical position. Base pay depends on your experience, most beginners start in the 50's and the highest I heard of was in the 70's. Depending on the contract and drug, bonus can be pretty good. I've worked a number of contracts with different contracting companies and have quarterly bonus be as high as 12K and as low as 200; it depends on the company they are contracting with, some are generous, others not so much. Few of the contracts will have you do programs, and that makes the job a bit less stressful. The contracts I've worked with Publicis give you a car stipend of $500.00 per month plus mileage (.19) I own my car so that makes it nice.
My last training had a large number of reps with over 15 to 20 years experience in the field and I was happy to see that many were over 50 yrs. old. As far as contract companies, my experience has been good with Publicis and Inventiv. PDI not so good and OnCall was pretty lax, but both of these were flex. I hope that helps, good luck.