All the major networks are being broadcast from Queen Anne and Capitol Hills, so I'd suggest you start with a basic antenna such as the RCA ANT-751. Avoid the use of an amplifier unless you need to run an unusually long run of cable and are feeding many tuners.
Attic mounting may or may not work for you, it will be a matter of 'try it and see'. The issue is not simply a concern about signal strength, but signal quality. Consider the difference between the image seen though high quality glass, versus the distorted image seen though scratched, dirty or translucent glass. While there may be a small difference in the total amount of light passed, your ability to see clearly is not just a function of getting light though, but passing the light with the least amount of scattering and reflection. Attic construction materials can scatter and reflect radio waves to the point that they can't be understood by the TV tuner even though enough signal power is getting though.
The ANT-751 is not likely to give you reliable reception of the signals from Orcas Island. StephanieS is quite right, reliable reception of KVOS will be far more likely if you opt for a high gain antenna outside, clear of obstructions. (I enjoy the MeTv programing carried by KVOS, so I have gone to the effort to receive it. I have an Antennas Direct 91XG + RCA TVPRAMP1R preamplifier pointed at Orcas Island.)
The near 0 NM signals are just low power translator signals (repeating KIRO or KCPQ) so there is no need to invest extraordinary effort for those.
The KCPQ signal on real CH-13, from Gold Mountain is not needed, you have an easy shot at their duplicate signal on real CH-22 from Capitol Hill. Folks are usually very committed to receiving religious programing or have no interest at all. The only other signal from Gold Mountain is the TBN affiliate on real CH-14.
My hope is that you will get reliable reception of the signals from Tiger Mountain as well, but until you try the ANT-751 you won't know for certain. Tiger mountain has ION and some less known network offerings that may be of interest. So, you may need to consider a second antenna, there are several way to incorporate multiple antennas into a system;
http://forum.tvfool.com/showthread.php?t=2882
http://forum.tvfool.com/showthread.php?t=820