I’ve done all three on the same day on several occasions. Being new to the Sierra puts you at a disadvantage, but doesn’t make it impossible. You could do Russell from UBSL or Iceberg Lake, back to camp, and then the Mountaineers’ Route. If you climb the Mountaineers’ Route, you can go down the trail to Muir, but you would have to hike almost all the way back to the Whitney Summit before descending back to camp. It’s fairly common to climb the Mountaineers’ Route to Whitney, and then descend the trail to the portal, tagging Muir on the way. However, this only works if you’re day hiking. BTW, in early October you may have just enough snow to make the rock a bit icy and much more difficult. Post again if my answer wasn’t clear or complete enough.