Well, if the actual site for the Cental Manchester station is on the Ordstall Lane site bwteeen Liverpool Road / Street and Deal St Junction, I'll be dissapointed, equally disapointed if the 'Manchester Parkway' station isn't able to serve Manchester Airport by means of moving walkways or walking. Theres tonnes of land that I have pointed out, and if they use it for businesses that couldn't care less if the're on Hardy Lane next to a pub, or shoved out onto some empty land near the T2 expansion area, then it will be a big waste of an opertunity.
Personally, I don't think three stations for Manchester is out of the question, neither is running into the Mayfeild Industrial area, theres many different routes to get there, and pathing a route from Manchester Airport, thats the easyest peice of spare land in Manchester to Access, Ordstall Lane would mean some tight curves and following the Alt'ham metrolink line. Granted, some Longsight access options have tight curves, but, it accesses Piccadilly, and therefore can be done in stages, with diversionary routes available.
You could for example run the route entirely above ground, with the destruction of about 40 private homes and 20 businesses. But it would mean tight curves, alternatively, 3 miles of tunnels and demolishing sainsburies would mean only sainsburys would have to go, or dive into a tunnel before there, in West Fallowfeild, just south of the A6010 and tunnel to Longsight, new viaduct from Longsight Intl. for 4 more tracks, 2 HS2 and 2 for the airport line. Would need a little bit of tunneling in Wythenshawe, a bit to get under Hardy Lane, and from Fallowfeild to Longsight.
Through trains, yes, they can call at Manc S Parkway or Manc W Parkway. Through the centre of Manchetser, I'd love to know what you'd been smoking if you can find space for that (I have, but it's all viaduct and would cost billions, and you may as well finish the M602 at the same time, as it will mean the demolition of a lot of businesses allong Regent Road.
And then there are two options for through routes, with my current prefered route into Manchester, either a tight delta junction near Sale Water Park, or a short tunnel under east Alt'ham, then pick up the old Stockport - Glazbrook alignment, and use their bridge embankments, meet up with the Chat Moss route for the WCML, facilitate for a flying junction to the north, Done.
Near Mauldeth Road West where the tunnel immerges from under Hardy Lane would be 3 track, with one track staying down the centre and above ground a little bit longer, then tunneling down under Hardy Lane to form a slack delta with a single track link to the north from Manchester. 2 track as soon as it immerges.
EDIT: Stealing some back gardens may result in enough space for a 2 + 2 track layout, but it would need to be in a cutting to dive under St Wellingrough's Road Metrolink Station.