Hello and welcome to Windows7Forums.com
I can provide some assistance here for you:
Question 1: By this I assume you mean the rounded corners on the START menu, correct? That's the only menu I've ever found rounded corners on in Windows 7. Via Registry tweaks or customization problems it is of course entirely possible to eliminate these rounded edges for pointed ones, or whatever.
Question 2: Of course
You have an RGB color slider in the desktop customization area that allows you to set virtually and colour and shade imaginable.
Question 3: Yes, in the same section as colour customization, you can set transparency from 0-100%.