Good luck with finding a house!!!
Unfortunately as it's getting very close, it may be very hard to find exactly what you want now and it is common place for landlords to ask for a deposit before you start.
About Kexgill, from what I heard seems to be one of the better big companies to go with and I've heard good things about their houses from friends with them. (Don't go with Unicom whatever you do) I believe their houses all have a cleaner that comes every so often though I think they only clean the communal areas, although the main downside to them I think is that none of their bedrooms have locks. They do seem to be reasonably reliable though and will fix any problems you have.