are you getting the property mortgaged? your lender will soon say if the lease isnt long enough. I think that they are usually fine if more than 50 years but you may have to increase when you want to sell.
you need to read the lease to find out if you can put an aerial up, some may say no, though unlikely. Is there not a communal aerial for the building, ask the vendor.
Building insurance is usually paid for by the management company or the freeholder but you will need to budget for your share and find out when its normally paid. Contents you will need to have.
Also check if you are required to pay to managment company for upkeep of communal areas and also when ground rent is due and at what cost