I always find that things are larger than I think they are in a picture. A 10" Dobsonian is rather large. The main mirror and optical tube diameter are about the size of a dinner plate and the height of it including mount will come up to around your shoulders when pointing straight up. 8" Dobsonians are, of course, smaller and therefore easier to move around.

If you're going to pick up a solar filter you should also get a Hydrogen-Alpha filter as well. It brings out a lot of surface detail of the sun.

Diffraction Limited and 'wave' is how precisely the mirror is ground. Wikipedia tells me that the definition of Diffraction Limited is "An optical system with the ability to produce images with angular resolution as good as the instrument's theoretical limit is said to be diffraction limited." I believe lower wave numbers mean the mirror is more precisely ground. From what ive been able to gather its how much imperfections there are in the mirror and how large they are. I think its in relation visible wavelengths (Around 550nm +/- 200nm) so 1/4th wave should mean that there are no imperfections larger than 137.5nm (550*(1/4)). Im not sure about the whole wave thing, so I could be horribly wrong.

Edit:
I just did some more research on this 'wave' thing. I checked out a book from the library, "The Backyard Astronomers Guide" by Terence Dickinson and Alan Dyer (ISBN 0-921820-11-9, Pages 51 and 269). Its short for wavefront error. For the most part I was correct, it measures surface defects of a mirror in relation to green light (~550nm). There is no agreed upon standard for measuring wavefront error (So one company could be measuring 1/20th wave on their mirror and another company could measure 1/10th wave on the same quality mirror) and most commercial telescope makers wont tell you wave numbers because its a measure of true optical quality. The wavefront error adds up in telescopes with multiple mirrors. If both the telescopes primary and secondary mirror is 1/8th wave then it adds up to a total of 1/4th wave over the entire optical system. 1/4th wave is usually considered the minimum to achieve perfect star images. According to the book 1/4th wave means diffraction limited. From what I've been able to make out professional astronomy optics typically have a wavefront error of 1/20th or less.