It is important to note that platforms like Musing.io and Steemit.com are only built on top of the STEEM Blockchain. This sites/apps are only UI's. This means all transactions (votes/comments/resteems,etc..) one will make on these platforms will still be recorded on the same Blockchain those other platforms are built upon and must adhere to the same rules and mechanisms that were put in place.
To clarify your questions:
1, Yes! It does bring down your Voting Power (-2% for a 100% vote) and will be the same worth as voting on other platform.
2. Yes! Since Musing is just built on top of the Steem Blockchain, All rewards you have gotten in here will directly go to your Steem Wallet. One great thing about Musing is that unlike other platforms, Musing does not take any beneficiary rewards or a cut in someone's payout.
Thank you! You answered my question perfectly