10 miles square is 100 square miles. The district is currently 68 square miles since land went back to Virginia.
As you can see here, the language of the 23rd Amendment states "if it were a state", thus a constitutional amendment would be needed to correct this if the land outside The Fed buildings etc were to be made a state. It can't be done with just legislation. The only move would be to incorporate these areas back into Maryland as was done with land retroceded back to Virginia before. If that was done though, you would still need a constitutional amendment to remove the Electors allotted to the district as several hundred people would now have too much power in The Electoral College.
Correct, but now you are going to want the new state and DC both to have Electors and that can't fly.
Something else to consider. --Rhode Island is an incredibly small state and it has 1500 square miles. Now, you want to make a state out of fewer than 70 square miles?====No way