A little advice? I strongly advocate for checking references and credit if you can, and having a lease...especially with "friends". This is, at the end of the day a business transaction, and I recommend you treat it as such.

I've seen too many situations turn ugly between "friends" when money is involved. Perfectly sane, reasonable adult people can turn into hysterical spoiled monsters with a huge entitlement attitude when they feel you should them slide on their rent during a rough month (or two or three or five) or not charge them for drilling holes in the plaster, or replacing the carpet they/the ferret/the orgy destroyed.
While it's an unlikely scenario, were it to happen, the hassle and vexation to you would be enormous. By treating it professionally rather than personally, it would protect all involved and remove the potential stress factor as much as one can. You don't need any more worries on your shoulders.

I would seek out some of our mutual friends who own and rent property already and get their advice as well. The mileage on my advice/experiences varies.