If you sort out the ground rules beforehand i think its a good idea. How long does he want to stay for.
Do you want them in your front room at night watching TV or in their own space. It sounds like they would be too busy to cause you an issue and I always find an extra meal on the plate/in the oven is here nor there as a inconveince. As long as if your not cooking its not expected. And it solves the issue of the room guest not being able to return. He is looking for about a year, but if it didn't work out it would be less. A months notice on either side I think is fair.
He won't be here hardly at all and the room would be like a bedsit for him to do study, watch tele, sleep etc. He will sort his own food and cooking and would have use of the kitchen, bathroom etc and can use the washing machine, cooker etc.
He is a lovely chap and I wouldn't mind him joining us in the living room sometimes if he wants some company.
I also know he is 100% trustworthy.
I just wonder how people have actually found the reality of someone in and out of your house, did it become a bind? Did you find you lost any privacy or was it nice having someone else in and out?