Calculation of tariff payments for all years

Hi. I have a question for the service team - I've been using the service for a long time on a free level, but I keep putting off the payment plan, but perhaps it's worth clarifying for me because of some silly questions.

1.If I have a trading history that is uploaded to the service goes back 10 years, and the number of transactions in different years ranged from hundreds to 3-5 thousand, and the total number of years is estimated in tens of thousands - I want to get estimated projections for capital gains/losses and balance sheets for each year. Does this mean, to cover the entire task a one-time payment of about 300-400 euros and this will open if necessary tax returns for each of the past years. Or is it necessary to pay one by one starting from the oldest year each year and it may turn out to be 2-3 thousand euros?

2.After payment, can the tax return pdf be downloaded only once or as often as i want during the year without adding payment (e.g. in case of adding new gathered transactions in previous years or making some transfer corrections)?