Self management is generally to be avoided except as interim measure. Usually dependent on active retired ex-professional - eg accountant - in the block. But then you have a big problem when they move on or simply want to retire completely. Also, awful problems can accrue with self management - such as arrears - which then ultimately have to be sorted out by a professional firm. Don't believe the above comments about all these firms being "dreadful" - and this probably refers more to leasehold situations, where the laws are much more lax. Remember that professional charges are still quite a small percentage of overall freehold costs - eg. insurance, water/sewage, gardening, general maintenance. More often than not, the problem is with some of the actual flat owners - who have blocked appropriate maintenance/modernisation/ repairs over the years - resulting in hefty bills or ill-feeling amongst other owners.
My first recommendation is to form a strong management board of realistic and like minded owners and then interview various firms to see if you can work together with them.