to answer the specific question in the OP:
yes, make clear (ASAP) that you will require a deposit and the month's rent in advance before you hand over the keys. I don't think letting agents will have deposits less than a month's rent, and neither should you (I paid six weeks). Don't do anything to give the impression you can be fucked about with, friends or not. Get on their case if they are late with rent. Keep it very businesslike.
yes, make clear (ASAP) that you will require a deposit and the month's rent in advance before you hand over the keys. I don't think letting agents will have deposits less than a month's rent, and neither should you (I paid six weeks). Don't do anything to give the impression you can be fucked about with, friends or not. Get on their case if they are late with rent. Keep it very businesslike.