Day 1: Nuke the filibuster
Yes. No question.
Day 2: Pack SCOTUS
Easily. Merrick Garfinkel will probably be the first of six installed. They need to up it at least 15 to overcome the conservative majority.
Day 3: Make DC & PR states
Once again that pesky Constitution is in the way and neither of these can happen without 38 states agreeing to it. The reasoning to do this getting four more guaranteed Democrat Senators and ending any chance of the Republicans winning via the Electoral College and to have a Democrat ran Senate. The only way they could get a "partial win" is to get a state to "annex" PR as another county. There is precedent for this as states have swapped territory/counties in the past. As for DC, not happening and even if they pulled their plan to shrink down the physical size of the capital to a couple of blocks and create a new state out of the rest, it still would require 38 states to ratify it.
EDIT: The ideal state would be one on 60-40 line and PR's spics would vote Dim to en masse to overcome the Republican vote.
Day 4: Enact federal takeover of elections/redistricting/campaigns
This would probably take a year but I suspect the quickest way to promise stuff and if that doesn't work, to just kill anyone standing in the way.
Days 5 - 36,500: Rule America uncontested for 100 years
Yep.