Toton seems the logical location to me, seems to be a lot of unused space, road access is good, would need a few chords for local rail connections, Tram would only need 1.5km of extension. Presumably the rusty locos

could be stored elsewhere (Long Marston?) if space were tight. Also Network Rail are building a new depot in Derby to absorb some local depots, so maybe some of their stock might move to Derby? (ballast cleaners etc?)
In principle thats a good idea but as close as the M1 is to Toton, buying up the land to build an access road would be very expensive and hugely disruptive.
In honesty (and bearing in mind that I was born in that neck of the woods), with an electrified MML and hopefully tilting trains I don't think there is really any justification in the East Midlands having an high speed line. I just don't believe that the numbers in terms of population justify it.
Apologies for going so wildly off topic!
The HS2 phase 2 documents state very clearly that there will be an East Midlands station. MML OHLE is all very well but the MML doesn't go to Heathrow or Birmingham International or Paris, so there are some significant journey time savings & hence market share to be gained here.
You wouldn't need an access road all the way to the M1- the A52 is dual carriageway & goes right over the top of Toton sidings. I think the section from Toton sidings to M1 could handle some extra traffic, might need some changes at the M1 junction. I suspect they might put in a link road along the site which would also connect with the A6005 in Long Eaton, though the 6005 corridor is quite congested.
The east yard area will cause some controversy, the landowner was already censured for felling the few acres of silver birch without permission, due to complaints from residents.
The greenbelt land between the sidings and the NET park & ride has a planning application for housing:
http://planning.broxtowe.gov.uk/(S(...))/ApplicationDetail.aspx?RefVal=12/00585/OUT
Which might rather mess up the logical tram route from the current planned park & ride terminus and the HS2 station, though the tram operator might prefer a slightly 'round the houses' route anyway.
However the planning app for houses, will be very controversial, and probably to to appeal & inspector, by which time HS2 Ph2 route will be published & station area protected ( I guess...).