When contracts call other contracts, there are four major parameters, g - gas, v - value, in - in size of inputs, out - out size of outputs. f.send(100) is safe since it sends only 2300 gas, but f.call.value(100)() is unsafe against reentrancy attacks since it does not have a gas limit by default. Anyone can table an investment proposal and vote over 14 days, 20-53% was a quorum to put the money in an investment.