I've rented a property out for 4 years now. I went with the managed option for the first year as I thought with property rentals being new to me I could do with the agencys assistance, frankly it was a waste of money. When the tenant had an issue they would contact the agency, who would then contact me if the issue or work required would result in the repair exceeding an agreed amount. With any costly work to be undertaken you should organise the quotes yourself as I would expect most agencies (not all) would have a list of preferred suppliers... if you know what I mean. During the first year the agency gave me a quote of £1350 for some work, I found a professional who did it for £650. I probably only save £40 a month by not having the property managed but that all goes into the kitty.
I've not gone with landlords insurance, I weighed it up and as with most insurance it wasn't worth it. I wouldn't put anyone off taking out insurance though. Probably the most secure payment you will find is when the rent is paid by housing benefit.
Have you looked at the mortgage deals for buy to let? Not a good market at present.