Montevideo is a great city. I really like it. It has a much more relaxed feel than Buenos Aires, it's quieter, the people are lovely, and it's not expensive. I would highly recommend staying for 4 days or so to really get the vibe of the place. But don't stay in the old city - it's grungy and perhaps the only place in the entire country where crime is of concern. I've generally stayed in the Plaza Cagancha area, which is a downtown neighborhood that's walkable to the old city and port, but unless you have a need to be downtown, it's probably better staying in one of the nicer beach neighborhoods by the Ramblas - Pocitos is a great option, as is Punta Carretas (near the eponymous mall).

I've never taken the ferry - just flights from AEP.

I was actually looking at going in late June, and it does seem Uruguay is opened up to vaccinated foreigners.