It depends on your skills. If you are good at the campaign, go for legendary. You should get about 3-4 pieces of armor. If you are good at following instructions, there are specific goals, such as Too Close to the Sun, in which all you must do is shoot something or complete something and it will give you the achievement. If you love multiplayer, there are skulls for it, too. You can also get the "goals" achievements, doing this. Finally, if you aren't good at any of this, you can easily get the Hayabusa armor by getting all of the skulls. You can go on normal and play through the game, finding the skulls along the way. That will give you the complete Hayabusa set.
The Vidmasters
easiest way is to download them through xbox live or get a bonus map pack in stores
The first one
The easiest way would be to go on other player's fileshares and download it, or if you have played it go on to recent games and download it there.
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3
i own it and halo reach is way shorter (but harder) then halo 3.
no halo wars is a rts(real time strategy). Halo 3 is way betteryes
The easiest way to do this would be to make some friends on Xbox LIVE and ask them to play, unfortunately i traded in Halo 3 when i got ODST, so i cannot help you.
The easiest way is to have shield doors floating to look like water. You can use active camos(instant respwan glitch) for smaller things.
its halo 3 of course halo 3 wins by1000000000% no way halo could lose master chief beats mega man
use the forge feature in any game after halo 3. In Halo CE, there is no way to do it.
There is no single "easy way" to get a Perfection medal in Halo 3, but be sure to remain calm and be patient. You will get one in time.