your questions are quite complex, whilst at the same time, the questions that most people face.
Firstly Genelec cover basically all of your questions in their "Step by Step" guide that you can download from the website. The owners manual also provides a lot of the info you require, you really need to read them.
The Monitor setup guide is indispensable for you, make sure you read it. http://www.genelec.com/catalogues-brochures/
As no one has provided any feedback frankie, here are my thoughts as how i would approach your room.
Your sub/sat placement decision needs to be based upon your workflow needs, for example, will you need to be able to monitor bass managed and also be able to switch to full range to the 8030's to check your mix?
Adding a sub into the monitoring chain provides a little more flexibility in the positioning of the 8030's in relationship to the front wall, however if you need to monitor full range in the 30's to check your mix, then you need to worry about the validity of the install without the sub.
My initial recommendation would to be to place the speakers as close to the front wall as possible, this will have the benefit of moving you closer to the front wall and thus further from the back wall. Speaker height is critical, i recommend the speakers be at least at seated ear level. For the sub i would start with it slightly off to one side of the centre of the front wall.
Once you have a baseline position it is time to calibrate, please read the owners manuals, all the information you require is at your finger tips.
Once the phase is setup, it is then a matter of matching levels and fine tuning, if you are interested in measuring the performance of your room, i suggest you download REW (windows), and have a play.
Don't get bogged down with information overload from the net, Genelec explain the physics of your speaker placement choices very succinctly, alot of the problems people worry about simply don't exist in many rooms, for example if your walls are light construction with little mass (plasterboard/drywall on a timber stud) the amount of reflected LF information is not very high, so room modes don't create the LF problems most people think. The opposite is also true, if you have high mass walls, then you are going to have many problems, it is here when a measurement tool will be critical.
At the end of the day, it is your room that dominates the what you hear, but with a little thought and time to fine tune your install you will get there.
As a guide the most basic recommendation i have is to sit closer to your speakers than any room surface, this will provide the highest ratio of direct to reflected signal, get your speakers up, just these2 basics have a profound effect, good luck and remember to have fun, when you feel overwhelmed, take a break.