It will use more on MacOS and Windows than on Linux, as it needs to use a sidecar Linux "Moby" VM to run containers. In practice on Windows, this hasn't been an issue for me (64GB RAM in my dev laptop).
This will actually finally change soon'ish with Windows at least, I think as part of WSL2. Not sure if anything is going to change on MacOS.
Not for me, except for the RAM blocking - I wish that Hyperkit could dynamically allocate and release RAM for the guest machine instead of blocking 2GB (in my case) by default all the time.