1) If you were to recommend a platform which one and why.
Using Peer-to-Peer (P2P) exchanges such as [1]
https://bisq.network/, [2]
https://hodlhodl.com/, and [3]
https://localcryptos.com/ are the most common suggestions. However, the issue with these exchanges is that the volume is low, making it difficult to find a seller of a whopping single bitcoin.
Furthermore, if you are new to these platforms, you may find it difficult to buy from other people as your account has no previous trading history especially that the amount you are buying can raise suspicion to other established p2p traders. Also, the country in which you reside is another factor to consider when purchasing bitcoin; the best solution I can think of is for you to look for an exchange in your country.
2) If I was to stake my 1 bit coin what would I get in return as a passive income.
Well? I think it defeats the purpose of bitcoin, no? I'd rather keep it in my non-custodial wallet than give other people the authority to use it.