I'm assuming you are in North America, as the Focus in Europe changed generations in 2005.
From my readings, the North America 2005 Focus received a "facelift" which, among other things, slightly changed the hood and introduced a new engine (the one you have).
This is not to say that a hood from a previous model year won't fit or won't line up, but they did change something about the hood in 2005, so you would be best to source a hood from 2005 to 2007. They did have slightly different body styles, so just to be on the safe side, you should get one from the same body style as sometimes it's not just the number of doors that changes, it's also the location and/or type of hood hinges and stuff. So, for the hood, get it from a 2005 ZX4, 2006 ZX4 or 4-door 2007 sedan (they stopped calling them ZX4 for 2007).
Same for the engine, the 2.0L engine introduced in 2005 was new. I can't find specifically what changed over previous years, but this engine became very common on 2005, 2006 and 2007 Focus models that are NOT the ST trim level. So, any 2.0L engine from 2005-2007 that does NOT come from a Hybrid (marked PZEV), as they have a slightly different 2.0L engine.
Hood from 2005 ZX4, 2006 ZX4 or 2007 4-door sedan.
Engine from 2005-2007 Focus S, SE or SES.
As far as salvaged or new, it's your call. Salvaged is cheaper, new costs more. New usually comes with a longer warranty, salvage is sometimes sold "as is," sometimes has a 30 day warranty. For body panels (your hood), salvage is already painted and you should be able to find one in your colour, new is often unpainted, so you'll need to paint it (costs more off the bat, plus the extra cost for paint). Keep in mind, this car is 12 years old, meaning the paint has 12 years of fade on it already. A freshly painted brand new hood won't match perfectly, unless you have some kind of paint genius artificially fade the hood paint to match the rest of the car.