namely those who were from the Marvel Universe rather than any other DC Universe resident, how well of an oiled machine could this version of the League be?

To note -- The MU recruits can only be those who live in the Prime Marvel reality and the recruiting will start soon after the Forever Evil event. Oh, and to be clear, whatever new recruits you want, they'll just be members of the primary JL team rather than any others.

Marvel JL team members that are my own:

Nick Fury (Sr.)
Elsa Bloodstone
Invisible Woman
Ant-Man (Eric O'Grady)
Blue Marvel