Regarding RAM consumption. I'm on a Windows box right now. The Windows Desktop Manager takes ~75MB RAM, but my Firefox process (with most tabs suspended) takes >2GB RAM. I run into the same on my Linux and BSD machines at home.

I run i3 and the XFCE settings daemon for convenience. Sure, I could optimize more, but it's really not the area where I'll see a lot of benefit. My best optimization for standard users is an automatic tab suspender.