Yes, the Staking Pool is shared by all Virtual AMMs.
Staking is flexible and can be done for any amount of time. A 14 cool down period applies when you begin the unstaking process. The length of the epoch can be adjusted through governance.
Some PERP rewards will be vested after 6 months. See Staking for more details.
The primary risk is exposure to volatility due to the 14 day cool-down period -- if the price of PERP changes in relation to other assets, you will be unable to swap it before the end of the cool-down.
In general, staking on Perpetual Protocol does not expose you to IL (impermanent loss) because you are staking a single asset. You can always withdraw the same number of PERP as you initially staked. However, due to the cool down period, the PERP token price may change before you are able to claim your tokens.