2004 Tahoe Questions?

Theres a few different qustions i have.. im in the middle of buying a new 04 tahoe and just wantto clear something up for when i actually get it..
first is the alarm system. i kknow that theres this new class b data system they are using. so i want to add a remotestart/alarm system. wit the widnow up/down option if i can. now i saw this site BYpasskit.com that has a module for this but theres about 5-6 listed for this truck alone. which one should i get??how do i use them??does it connect to the alarm and the one wire connec to the truck??anyone use them???

and for the other part of the question

i have an alipnne cva1003 i have in my truck now that im going to takeout and put in the tahoe. now if i get teh tahoe with the built in dvd system. how dod i tap into that to play thru my screen upfront??
can i do that. also i need the pac aonstar interface for this right? but it says i loose the dvd whats that mean i cant get any audio then??
please let me know how do get by this

thanks for all your help sorry its so long

ok i gotthe Z withoutthe dvd which makes it easier on me nmow but i still have afew quest. the alarm quest are the same but what do u think of the DEI 544R?// but now i have the radio quest???

-- is there anyway that i can use the stock XM antenna for my alpine xm reciver???

-- will the rear radio controlls work wit hthe new radio?? and will the pac sterring wheel interface work on the new 04 tahoe for my radio?? nothings going to change if i pull outthe stock radio right. aslong as i get the onstar and bose interface right??
please help im getting it this week and i wantto start work on it
thanks please help