What is the minimum amount of coin needed for PoS?
I think the minimum is 100. But don't even expect to be rewarded with some PoS blocks with this amount. For my analysis, the minimum amount to have some PoS blocks sometimes is 10.000 coins.
From my memory, I can quote Chekaz (or another member, not sure) :
Consensus seems to be that TZC staking is rewarding about 15% per year. A block is worth 100 coins. So for example if you had 100,000 TZC you would expect to gain around 15,000 TZC in a year, which is 150 blocks. There are 365 days in a year, so you'd average a block every ~2.43 days.
So, if you have 10,000 coins you can expect one block every 24 days .... remember it's a probabilist calculation ;-)
The 15% a year is given is just a matter of "when" or "how often" you find a block but regardless I will still have the 15% a year?