I appreciate your enthusiasm for fragrances! I was the exact same way when I first started this hobby. But be forewarned: don't buy blind based on what others have to say because I regretted a lot of my purchases this way. Buy samples and go with what you like. Let's see if I can answer a few of your questions...
When I spray my neck or wrists, I let the cologne evaporate naturally. I believe that it lasts longer this way. When you rub it in I find the top notes fade rather quickly.
Sillage is a french term (pronouned see-yij). It's used to describe how a scent lingers in the air. Fragrances with a lot of sillage such as Joop! and A*men can still be detected after the person has left the room. I also consider this term to describe how well a person can detect a smell on you. So in both regards to radius and scent trail, they are both correct.
A signature scent is a frag that we use the most often in our rotation. Certain scents are only used for specific purposes depending on the occassion or season. A signature scent is used throughout the year and is versatile for almost any situation.
A gourmand is a term used to describe scents which resemble food such as chocolate, vanilla, caramel, etc.
I get accustomed to almost every scent with the exception of strong ones like Le Male, Joop!, and A*men. Platinum Egoiste is my signature scent but my nose gets "immune" to it after about thirty minutes. I can't smell it anymore but I continue to receive compliments throughout the day so I know it's still there. It's a rather light scent so I don't expect it to last more than 4-6 hours on my skin. I find it very suitable for the office as it's not overpowering or offensive. Resist the temptation to overspray though.
As for your recent purchases, I personally like Silver Mountain Water and Himalaya, although I find that I get "immune" to these scents after only ten minutes.
Hope this helps and please post your impressions/opinions on your lastest purchases. I like reading what others have to say. Good luck.