#1 Bad workmanship or little knowledge of vehicle, either or.
#2 Im not sure about that one but some vehicles have a factory hoodpin that can be connected to. The silverados dont that I know of but idk about the Cobalt. They are usually hooked up but since most systems also have a under dash switch to disable the remote start occasionally the are avoided. Still good idea tho imo. Only reason I would avoid it is if I couldnt find a suitable spot. Warning sticker that should be under the hood for the system should notify of the dash switch.
#3 I avoid the horn unless asked. wizes too many people off. The trunk is a feature usually. Yes its almost always easy but some people dont want it and think that by my not connecting it they will get a huge discount. So I bill for it. Im not gonna do a job where a huge chunk of my pay gets taken because someone didnt want the trunk. Sorry but we do need to make money too. Honestly I do try to include it as much as possible tho and make it cheap.
#4 Turn your vehicle off with the key and dont have any doors open and dont get out. Your radio should stay on too. Its a feature. If you dont like it, connect the door pin switch to the arm wire. That will make it think you opened a door. Radio usually shuts off after five minutes or so anyway tho. Not likely to be an issue, imo.
#5 IDK what you mean by "Priority door access" but if you mean one door unlocks then the other depending on how many times you push the unlock button then its an option. Alot of guys I do jobs for get upset when it doesnt both unlock. So I just program the remote starter to pulse unlock twice and thus unlock both doors at once. Again its an option and can likely be changed.
#6 Dont lock your doors with the key, with the button inside or with the factory fob. You set the factory alarm off, not the remote starts alarm. If I left someone to guard a bank and said only let me inside, noone else, if someone else tried call the cops. If I came back in a disguise the guard would call the cops. Same thing. Your setting the factory alarm when you lock with the key then setting it off when you unlock and open with the remote starter remote. Most security modules handle that but not all. Again it can probably be remedied but I dont do many Cobalts and I dont ever use ProStart.
#7 ProStart, at least in the past, has interesting responses to cold weather. One fun one was relays not disengaging. It makes toast out of your starter in a hurry. Make sure you have anti-grind. To do this try cranking the vehicle when its running. If it doesnt scream at you, your good. If it does, well Google ProStart and make sure they fixed their issues. Personally I dont do them and wont.
#8 Im sorry about the trouble your having and hope you get it solved with no further issues. The thing with the systems is they have a lot of features and it depends on the shop and installer which they think should be hooked up and which shouldnt. Sometimes legal issues are of concern, sometimes experience with past customers, sometimes some features are just useless, bad or pointless. Some just are not usually needed and in order to remain competitive we cant hook up unless you are willing to pay for the extra option. Freemarket economy for you.
Nice present btw. Take care dude, hope I helped a bit. :)