fitting an alpine head unit

[custardsastra]

hi all

im new on this site and only just got my first astra what i would like help with is fitting an after market head unit as i do like my music 

my first option would be to fit a sat nav unit like the alpine ine w990bt this requires a speed pulse signal for more accurate position on the unit where would i find the speed pulse wire to tap off??

i could forget sat nav and go with an alpine ive w585bt to fit both of these i will need to change the fascia is this a pig of a job or not to bad to do??

how much info will be lost on the top screen if i go ahead and do this install will the steering will controls cause problems the fascia is a connects2 model with all patch leads

i will also replacing the speakers and adding a sub are the door speakers a nightmare to do ? has anyone run a new loom for the door speaker or is it better to use existing loom?? 

thanks for any replys as im sure i will be asking more questions in the coming weeks as i progress