I can help with two of these but I'm not sure what you're asking for in Q.2.
1. Go to File> Preferences> Units & Rulers change the units to display measurements in Pixels.
Open your 'Info' box (Window> Show Info) when you draw your line the info box will show you the start and finish XY coordinates in pixels, from which you can work out the length alternatively use the Guides and the Rulers (you can drag the rulers to your guides to give you X0 Y0 coordinate where you want your line to start).
2. Choose the type of gradient tool you need from the toolbox (Linear, Radial etc). Choose foreground to background option and normal on the operation. Click the Edit button on the gradient window. Edit the colours by highlighting the tab and going to the colour picker within the dialog box. Add the extra colour you need by clicking on the gradient bar (drag off any you create by mistake). Drag the tabs around to get the grad you're after.
Alfie.