How many coins needed for run a node?
You can run a node with no coins. There is no minimum for staking, but would probably need several thousand to make it interesting. Wallets staking 100 coins, or less, have published blocks and won block rewards, but that is rare.
What technical (VPS) requiments for run a node
About 2 GB RAM and 10 GB disk. On AWS, t2.micro with a swap file
Qtum AMI, on Google GCP g1-small
Qtum-Core VMhow much is annual ROI?
This depends on Network Weight, the total number of coins being staked, and is typically in the 5 6% range. See the
stake calculator for the current ROI and to try some different stake amounts.
As I see 96 mln out of 107 mln are in circulating right now... so rewards for nodes will end soon?
The first halving will be in early December 2021, and the last block reward subsidy will be in 2045. Stakers (miners) also receive the transaction fees and Gas.