The Turkish Land Forces have 315,000 men, large number of conscripts that serve one year terms. Their premier unit, the 3rd Corps, is a mechanized NATO Rapid Deployment unit. The Turks don't have too many commitments abroad so their troops are available for response to Russian aggression. I highly doubt that the Russians could scrounge together enough men to take Istanbul and the Bosporus. Attacking Turkey would also mean Russian trade from the Black Sea would be cut off, eliminating the utility of taking the Crimea in the first place. If Putin were to go to war with the Turks, he would truly be a madman.
Not saying it was a good plan - just wondering if Russia would attempt to pressure Turkey on their shared border.