1) any ditribution of linux will run on any dell, but not all the components will work. if the hardware is supported in the linux community than it will or if you buy a dell system that comes with linux pre-installed, the hardware will work.

2) again, it all depends on the hardware. in my ibm thinkpad a21m, everything works in every distribution i have tried (7 and counting), however, my dell inspiron 3500, the sound doesnt work (still trying to figure this one out). for desktops, i never buy pre-built systems and build my desktop myself. this insures 100% compatibility because i review everything that i plan on buying and make sure that its supported in linux.

3) the thing with linux is, not to go off recommendations, but rather, try them all and stick with what works best for you. a lot of people recommend ubuntu while i would recommend fedora or slackware (depending on how well you are at learning). not everyone learns at the same speed. some like to be eased into a new product while others like to just dive right in. so, you should try them all and stick with what works best for you.

4) your final statement is rather irrelavant because every distribution of linux can do all of that.

I agree with trying as many different Linux Distro's as possible. This is pretty easy and painless now that many Distro's are available as live cd's that will run completely from the cd without installing anything on your hard drive. The one that I would recommend that you try is SimplyMEPIS 6.5, the ISO for the live cd can be downloaded from mepis.org. It does an outstanding job of detecting and setting up hardware automatically.