We were scheduled for the Best of St Petersburg tour in 2020 and planned to take the train from St Petersburg to Moscow for 4 additional nights, 3.5 days:
Arrival evening: Bolshoi Ballet (some performances sell out, others do not, best to buy tickets in advance if you are keen)
Day 1 (a Thursday): Moscow Metro Tour; Pushkin Museum of Fine Arts (late opening on Thursdays, pre-COVID)
Day 2: City Walking tour
Day 3 (a Saturday): Moscow Kremlin Tour with private guide; Ceremonial Parade of Horse Guard and Foot Guard
Is Moscow too ambitious for only 2 or maybe 3 days?
You may wish to research the Moscow Metros to see if you want to include time for them; the Stalin government spent billions to create the underground "palaces"
Should I be concerned (as a female) about solo travel to Moscow?
I usually travel solo but we had planned to hire guides for each of our major activities. We were working with Marina Penkovskaya, as recommended on the tour FAQ page. She was incredibly responsive and provided helpful recommendations, even for the ballet tickets that we booked independently.
I did study the Russian alphabet and a few Russian phrases so that we could at least recognize a few signs.
is there a way I could connect with others on my tour prior to ask if anyone else is heading to Moscow?
We were scheduled to be on that tour this year, but had to cancel. Shame, it would have been fun to connect!
The last time I checked, all but essential personnel had left the Moscow embassy (that was the case even before the current Ukraine situation) and the embassy website said that they could offer passport services.