I believe that the Imperial fists and a very small detatchment of space wolves are the only space marine forces allowed on terra.
As for the PDF id imagine that it is larger than any other pdf in the imperium and as stated above is more than likley larger than many crusading imperial armies. So thereforce probobly 1 billion plus actual soldier and then the quite real possibility of everyone on the planet being conscripted in times of need.
Then Battlefleet Solar is descibed as the mightiest battlefleet available to imerial forces so would probobly number into the thousands if not tens of thousands of ships of all sizes. And then all the defense instillations in space, on luna and then on terra itself.
Then theres the mechanicus of mars so there will be a number of titan legions along with all the tags alongs that come with them (skitarii and techpriests etc) numbering into the millions.
Theres also the inquisition and their available forces. I suppose you could include grey knights that would be available to defend terra.
Im sure theyll be some sisters of battle around on terra not too sure how many though.
Each navigator house has a small private army so they would probobly be used to defend terra.
Not forgeting the custodes but they only guard the palace so yeah... probobly numbering a couple of thousand.
So in conclusion theres a hell of a lot lol!