As you can see there are plenty of people here that are willing and able to help you out.
You now have a decision to make
OPTION 1
Pay a pro (agreed stereo installer or maybe auto-electrician your best options)
Positives are that it will be fast and safe.
Negatives, you will likely learn very little
OPTION 2
Get ready to learn, and do it yourself, I promise it is nothing difficult.
Positives is some “great” learnings for you and you will get our admiration and respect 
Negative, will likely take longer
OPTION 2.1
Do MOST of the work yourself (installation and wiring), get the pro to finish it off by picking up and connecting power
Positives same as option 2, will save money in labour from Option 1
Negatives, again likely slower
NOW I REALLY HOPE YOU GO WITH DIY OPTIONS, OR I AM GOING TO WASTE A LOT OF TIME WRITING THE NEXT BIT UP
What is wrong with your key fob? @turbo2ltr
May have another option for you ( The same one @ODaily linked to above )
If you choose to use xAC V2
REMEMBER, there is more than one way to skin a cat, but this is along the lines of how I would do it.
Start taking notes, electronic or written form, for your own reference ( and also to do a project write up at the end, and don’t forget photos 
, photos can also help if you start changing things around with wiring ets to get you back to a baseline if “you fuck things up” )
Make yourself a workspace to do a bench test and learn how it works check out this link for an idea
Get together some basic tools:
For this install, the list can be quite short, some things will be essential, you might need to do some sums, and the cost for a pro to install may be less/ ~same/ more and you might change your mind, bearing in mind, you will then own those tools and can do more projects in the future
Others you can get by without.
Just a quick mind map ( some things you will be able to use alternatives / work arounds)
None of this needs to be expensive, but you often get what you pay for ( I have heard it mentioned many times on here, I am not personally familiar with it, but in my mind at least, harbour freight quality should be fine.)
Multimeter
Sidecutters / wire strippers
Soldering iron / solder ( could use crimps and crimp tool but personally think soldering is better general purpose )
Heat shrink (electrical tape)
Cable / wire a few meters of red and black ( ~24 awg )
Fuse and holder
12V load ( LED or lamp etc ) for bench testing 
Automotive relay(s) if you want to be able to unlock AND lock
A workshop manual for your car may be helpful, but Google and “common” wiring may help out here and can be tested with a multimeter
This list could keep going, but that SHOULD be enough to get you up and running.
Others will probably jump in with something I have omitted, to which there isn’t a safe workaround.
9-12v power supply (battery / wall plug) 12V Battery probably better for portability!?
I don’t have the V2, so hopefully somebody can confirm if a 9V battery will operate the unit for testing, personally I think the 12V will be better for this
From here, watch the xAC V2 video
Replicate on your bench, ( add a fuse on the positive wire between the power supply and the xAC) enroll your implant, ask here if you have any questions.
So what you will notice we are doing here is breaking things down into manageable bites
Now you are ready to get into the vehicle [pun] side of things.
Planning will help you out here
As you stated the windscreen or wing mirror are likely your best / easier options for antenna placement. but you will want to test them in situ, to make sure you can read your implant through the glass or plastic
Find a location to put the xAC unit within the length of the antenna cable run (in an enclosure eg. the 3d printed enclosure link by the dingo brothers @PulsarForce and @Compgeek), For everything else you can easily extend the cable length if required.
Put the fuse somewhere accessible, or if you can access it, pick up a spare fuse socket on your fuse panel
If you were to install up until this point and weren’t comfortable with the following steps, it would be a good place to get the pro in to finish it off and power it up. ( They will probably do something similar as described below )
Now the slightly more tricky part, mostly because at the moment we have some unknowns:
Your door locks and how they operate.
There are 2(3) main “types” Positive pulse, negative pulse and vacum ( unlikely )
If you had a workshop manual for your car this would help about now, otherwise, a multimeter can be used ( and should be anyway to confirm)
To identify
In the drivers door should be the master door lock switch, if you can pop that out, that will make things easier, otherwise you may need to remove the door card to get access to the wiring / underside of the switch.
Man, this could take a while to explain… Do you know how to use a multimeter?
I ( Or somebody else ) might find you a good youtube video if.you need one
I might leave it here for now, until after you have answered the few questions throughout my ramblings above and below
Plus there are a few things to cover, like fuse size, how to earth, does your car sit for extended periods of time