Can I PoS mint in simplewallet? Or have I to use GUI?
Sure, you can use simplewallet for staking:
simplewallet --rpc-bind-port=yourport --wallet-file=path\to\your.file --do-pos-mining --deaf
--rpc-bind-port - this needed to launch simplewallet in server mode
--do-pos-mining - this tells wallet to launch staking
--deaf - tells simplewallet to ignore any network rpc requests (for safety reasons)
--deaf huh, interesting trick, didn't know that one!