You're gonna get lots of answers on this... My .02 is below, in colors.
1. You want both control arms to be level with the ground, when the car is at ride height and at full weight,IE. ready to drive down the road. You want the lower control arms (LCAs) level with the ground. Uppers typically slant downward slightly from hub to chassis.
2. Upper control arm length to lower control arm length typical ratio? If the upper control arm is 12" long from mounting point to ball joint, then you want the lower arm to be around 18" long. then build in adjustments for caster and camber.I'm not aware of a "ratio" per se. That does NOT mean there isn't one. Typically, you experiment using a "string computer" or a software package like the ones mentioned in various threads in here (Wishbone, for example) to define control arm lengths based on desired track width and camber gain.
I under stand all this is just for a basic guide line, but I am almost ready yo start working on the layout of my front suspension
What would happen if the lower control arm is level and the upper control arm in built to be in an angle downwards from the mounting point to the ball joint?I don't know exactly what this would do to suspension geometry, but I think it would do strange things to your roll center height. Other folks can likely answer this better.
You might want to "study up" a bit on suspension geometry before you go to much further. As soon as I remember the title of the book I used as my main reference, I'll edit this post and put it in here. You need to figure out the geometry of the front end, calculate the instant centers and roll centers and such. The design of the front end, especially the angles of the control arms, will make a lot more sense then.