Not from Germany but close by, so I should be able to give you at least partial answers:
- Can you be more specific if that also includes: masternode, stacking, lending...
The way staking, lending, etc. gains are being taxed has been a contentious matter over the years (supposedly it was unclear whether the 1 year holding timeframe would apply for coins used in staking and lending or whether the timeframe would be 10 years in this case) but as it stands the situation seems to be as follows: No tax on value appreciation after 1 year of holding; however the staking profits themselves get taxed as income, similar to mining (since that would make the taxation rate of mining, staking, lending, etc. the same I don't think there's a practical difference). Where it gets complicated is that the staking / lending profits are EUR-based so to determine your taxation correctly you need to keep track of the EUR-value of every single staking / lending payout you receive, which may cause you to pay taxes on unrealized gains. After that you then also need to pay taxes on any gains gained by appreciation of your coins, unless of course you hold them for at least 1 year.
- Does it also apply to a company? Let's say a company has its own activity (selling shoes) but also invests in the crypto sphere. Whatever if it's to 'hodl' 365 days, masternodes, and other ways.
Tax-free gains after the 1 year holding period don't apply for companies. If the coins are part of company holdings, realized gains will be taxed regardless of the holding period.
- In my country, the citizens need to report every year each account they have with exchange platforms (even closed accounts). Do you have something like such there?
I've never heard of anything like this from the German Bitcointalk members, but I'm not sure to be honest.
- What document do you provide to prove that you bought the coins 365 days ago?
In theory it should be sufficient to just provide your on-chain information. In practice one can run into a problem of technical ineptitude depending on which clerk is handling your case, with multiple back-and-forths required until the matter is settled. In the end on-chain information should be enough though (although it's definitely a good idea to also have records of your exchange trades and transactions, which some banks might even require once you get onto their radar for handling cryptocurrencies).
For reference, in case you haven't seen it, here's the German Tax thread:
https://bitcointalk.org/index.php?topic=1976285.3340