1) The boot lid does not self-raise. I looked into achieving that by fitting stronger gas struts, and while they did actually open the boot lid at the press of a button, albeit slowly, they also made it a Herculean challenge to push down & close, requiring two hands...
The original gas struts are exactly enough to keep the lid in place, not letting it raise up nor go down by itself. If yours doesn't stay in place when like half-open, you might look into replacing one or both of the struts.
2) None that I know of. Since you have the cassette player, consider doing this extremely handy mod (unless you have ACM installed that is).
3) The later-style grille does look good with the pre-facelift front bumper. It is one of my planned upgrades. However, I won't be buying the OEM 2008+ grille, for I dislike the idea of chromed plastic mesh and a fixed spot for the badge. See the ones below, the one on the left is the OEM plastic grille, the one in the middle is a new-style grille by Mina Gallery (which I like), and the one on the right is an earlier "new-style" grille by Mina Gallery with a denser mesh.
4) If you do put a leaper on, do as I did and buy something like this copy version. It is spring-loaded (and actually moves more easily than the OEM leaper), and attached with dual-sided super strong 3M tape so it does not require drilling holes in the bonnet. I fitted one on my car one month ago and it stays on like it's set in concrete. I call it "the copycat" :D
If someone complains about it and you have to take it off, you'll have a pristine bonnet underneath rather than two mounting holes to fill & paint. The only real difficulty with this one is that without the mounting holes to guide you, it takes some effort to measure and see that you put it in the right place & that it's straight. I put mine slightly further forward than the original ones because I found that it looks better that way.