It's certainly an "interesting" time to be investing in BTL property, when most experienced landlords are getting the hell out!
We have had BTL properties for a couple of decades and will be selling up in the next two or so years. Assuming you are set on this means of investing my thoughts would be:
yes use an experienced agent - btw, full management fees are about 15%, not the 10% mentioned above! Ten percent will only get you a new tenant and the checks on them but not ongoing management. Because of our long-standing relationship with out agent and because we have more than one property we get a rate of 11% but they keep attempting to change that;
if you don't live close to the property and you don't have lots of good reliable tradespeople - plumber, LX, handyman etc on hand, don't even think about managing yourself;
hopefully you have a comprehensive spreadsheet and have worked out ALL the costs involved in letting and any fallow periods. You need a float of money to allow for any works which need to be done, including large works which may be urgent such as replacing a boiler. You must have regular gas and LX checks. Your smoke alarms must always be in date - and if they aren't, don't think you can just ask the tenant to replace them! If you don't live close to the property, you will be charged the base rate to send a handyman around to do it so your £10 replacement will end up costing probably £80. Again, if you don't live close to the property, anything like a blocked sink, a loose door handle etc needs a contractor, rather than the plunger that you would probably try yourself if you lived there. Generally, you need to redecorate every 5 years and re-carpet every 10;
don't forget your tax liabilities!
It is very difficult to get money back from tenants for repairs/maintenance which may be due to their lack of care. We had sinks which were blocked a month after a tenant moved in which would seem to be their fault for pouring fat etc down the sink but impossible to prove because they will claim it was a build-up from the previous tenant.
Using an agent will remove at least some of the time/advertising/checks element from finding a new tenant but comes at a cost - now that costs cannot be passed on to tenants, agents charge hundreds of pounds for new tenancies, plus charges for check-in and check-out inventories. You are also liable for council tax, utilities etc for any period between tenancies.
It is already a process of months to get rid of non-paying tenants or those who refuse to leave at the end of a tenancy. The imminent advent of the Renters Rights Bill may make that even more difficult.
I think the fact that so many experienced landlords are leaving the market should give you pause for thought at this time. The bottom has certainly fallen out of the flats market, I know you are buying a house and there are still lots of landlords about but unless you really know what you are doing I think this is completely the wrong time to get into this.