1) Smaller file size is a negligible advantage nowadays IMO. 2) Yep, that's usually true. 3) Surely you are joking! Any half-decent text editor that lets you choose spaces for indentation will use the tab *key* for indentation, but producing the right amount of space *characters* on the file. It will also support autoindent, and maybe even "smart" autoindent (although I personally hate the latter).
In my experience, although the argument for tabs is pretty logical, it doesn't work that well in practice. Years ago I thought a lot about the issue, decided to use tabs, and configured my system accordingly. It ended up being a lot of trouble whenever I interacted with anyone else or got source code from anywhere else. Even without interacting with other people's code, I had trouble because I was using a variety of programs on a variety of platforms, and not all of them let you configure the tab stops (or it wasn't worth the time). I switched to spaces and I've been much happier ever since. :-)