An alternative (perhaps cheaper) to buying the freehold might be to get the right to manage:
http://www.direct.gov...dproperties/DG_193051
Also, it is worth contacting the Leasehold Advisory Service (link in the above article) for advice - partly because you must get hold of proper accounts to show what has happened to the service charge money you have been paying.
More importantly, you should also ask them how the 25% commercial rule is calculated. Is it based on the number of units (i.e. the number of shops compared with the number of flats) or is it based on the square footage in total of the shops compared with the square footage in total of the flats? You must do this at an early stage because you might find that you do not qualify for the right to buy the freehold or the management. If that is the case, you need to ask them what steps can be taken to make the freeholder accept his responsibilities & carry them out.
Whatever you do is going to involve a cost, & the cost of the major repairs that are needed is almost certainly going to have to be met by the leaseholders. This may cause you problems as some of them may genuinely be unable to afford it.