Well, I brake and downshift, I don't think I'd ever downshift to a stop without braking unless it was an emergency.. Apparently it does damage to the engine too, which I'd believe, revs jumping up insanely..
Anyway, as for when to change gears, you'll be able to feel when your cars not powering on anymore, watch your tacho if there is one, you'll only need it for a few weeks if you don't, just until you get used to the sound/ feel of the car when its on the limit.
Downshifting, well, to tell you the truth I don't think I've downshifted into third for a while.. Most of the time I just go fourth/ second.. keep rolling if the light changes, or 1st if I stop.
Same with upshifting, if its a cruisey day I'll just go second to fourth.. Hell its easier..