Ask to see the accounts for the last 3 years.
Ground rent is typically nominal, I think mine is £50 per year but it does increase in line with the lease. If I live to be 150 then I may be paying £400 per annum.
Beyond that there should be service charge account to cover repeating costs insurance, communal lights and heating, cleaning, gardening, and minor repairs. Any service charge service at the end of the year cannot be retained and should be deducted from next years service charges. But sometimes the leaseholders may agree to transfer it to the sinking fund.
The sinking fund is used for major works and money can be retained year on year. Generally the lease will provide a clause that enable the freeholder to ask for extra to cover large urgent costs that cannot be met from the existing sinking fund e.g a new roof ours cost £600,000!
Depending when the lease was drawn up then you will need to accept some latitude in how the accounts are used. To exercise my lease to the letter of the law would not be pragmatic. But my residents association of which I am a 1 / 32 shareholder will do their upmost to hold on to my money. Pees me right off at times
Ask to see the lease, and read it carefully.